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  • 1. PrefaceA well-developed knowledge of clinical microbiology is 4) Create a conceptual, organized approach to the or-critical for the practicing physician in any medical field. ganisms studied so the student relies less on memoryBacteria, viruses, and protozoans have no respect for and more on logical pathophysiology.the distinction between ophthalmology, pediatrics, The text has been updated to include current infor-trauma surgery, or geriatric medicine. As a physician mation on rapidly developing topics, such as HIV andyou will be faced daily with the concepts of microbial AIDS (vaccine efforts and all the new anti-HIV medica-disease and antimicrobial therapy. Microbiology is one tions), Ebola virus, Hantavirus, E. coli outbreaks, Madof the few courses where much of the "minutia" is regu-larly used by the practicing physician. Cow Disease, and brand-new antimicrobial antibiotics. This book attempts to facilitate the learning of mi- The mnemonics and cartoons in this book do not in- tend disrespect for any particular patient population orcrobiology by presenting the information in a clear andentertaining manner brimming with memory aids. racial or ethnic group but are solely presented as mem- Our approach has been to: ory devices to assist in the learning of a complex and im- portant medical subject. 1) Write in a conversational style for rapid assimi- We welcome suggestions for future editions.lation. 2) Include numerous figures serving as "visual mem- MARK GLADWIN, MDory tools" and summary charts at the end of each chap- BILL TRATTLER, MDter. These can be used for "cram sessions" after theconcepts have been studied in the text. 3) Concentrate more on clinical and infectious dis-ease issues that are both interesting and vital to the ac-tual practice of medicine. D
  • 3. PART 5. VERY STRANGE CRITTERS 26532 PRIONS (contributing author: Hans Henrik Larsen, M.D.) 265PART 6.33 ANTIMICROBIAL RESISTANCE: ONE STEP TOWARD THE POST-ANTIBIOTIC ERA? (contributing author: Earnest Alexander, Pharm.D.) 269BIOTERRORISM DEFENSE UPDATES:http://www.medmaster.netBioterrorismDefense.html
  • 4. PrefaceA well-developed knowledge of clinical microbiology is 4) Create a conceptual, organized approach to the or-critical for the practicing physician in any medical field. ganisms studied so the student relies less on memoryBacteria, viruses, and protozoans have no respect for and more on logical pathophysiology.the distinction between ophthalmology, pediatrics, The text has been updated to include current infor-trauma surgery, or geriatric medicine. As a physician mation on rapidly developing topics, such as HIV andyou will be faced daily with the concepts of microbial AIDS (vaccine efforts and all the new anti-HIV medica-disease and antimicrobial therapy. Microbiology is one tions), Ebola virus, Hantavirus, E. coli outbreaks, Madof the few courses where much of the "minutia" is regu-larly used by the practicing physician. Cow Disease, and brand-new antimicrobial antibiotics. This book attempts to facilitate the learning of mi- The mnemonics and cartoons in this book do not in- tend disrespect for any particular patient population orcrobiology by presenting the information in a clear andentertaining manner brimming with memory aids. racial or ethnic group but are solely presented as mem- Our approach has been to: ory devices to assist in the learning of a complex and im- portant medical subject. 1) Write in a conversational style for rapid assimi- We welcome suggestions for future editions.lation. 2) Include numerous figures serving as "visual mem- MARK GLADWIN, MDory tools" and summary charts at the end of each chap- BILL TRATTLER, MDter. These can be used for "cram sessions" after theconcepts have been studied in the text. 3) Concentrate more on clinical and infectious dis-ease issues that are both interesting and vital to the ac-tual practice of medicine. D
  • 6. PART 5. VERY STRANGE CRITTERS 26532 PRIONS (contributing author: Hans Henrik Larsen, M.D.) 265PART 6.33 ANTIMICROBIAL RESISTANCE: ONE STEP TOWARD THE POST-ANTIBIOTIC ERA? (contributing author: Earnest Alexander, Pharm.D.) 269BIOTERRORISM DEFENSE UPDATES:http://www.medmaster.netBioterrorismDefense.html
  • 7. PART 1. BACTERIA CHAPTER 1. BACTERIAL TAXONOMYAll organisms have a name consisting of two parts: thegenus followed by the species (i.e., Homo sapiens). Bac- DISACCHARIDEteria have been grouped and named primarily on theirmorphological and biochemical/metabolic differences.However, bacteria are now also being classified accord-ing to their immunologic and genetic characteristics.This chapter focuses on the Gram stain, bacterial mor-phology, and metabolic characteristics, all of which en-able the clinician to rapidly determine the organismcausing a patients infection. GRAM STAIN Because bacteria are colorless and usually invisible tolight microscopy, colorful stains have been developed tovisualize them. The most useful is the Gram stain,which separates organisms into 2 groups: gram-positivebugs and gram-negative bugs. This stain also allows theclinician to determine whether the organism is round orrod-shaped. AMINO ACIDS For any stain you must first smear the substance tobe stained (sputum, pus, etc.) onto a slide and then heatit to fix the bacteria on the slide. There are 4 steps to the Gram stain: Figure 1-1 1) Pour on crystal violet stain (a blue dye) and wait60 seconds. 2) Wash off with water and flood with iodine solu-tion. Wait 60 seconds. Both gram-positive and gram-negative organisms 3) Wash off with water and then "decolorize" with have more than 1 layer protecting their cytoplasm and95% alcohol. nucleus from the extracellular environment, unlike an- 4) Finally, counter-stain with safranin (a red dye). imal cells, which have only a single cytoplasmic mem-Wait 30 seconds and wash off with water. brane composed of a phospholipid bilayer. The layer just outside the bacterial cytoplasmic membrane is the pep- When the slide is studied microscopically, cells that tidoglycan layer or cell wall. It is present in bothabsorb the crystal violet and hold onto it will appear gram-positive and gram-negative These are called gram-positive organisms. How-ever, if the crystal violet is washed off by the alcohol, Fig. 1-1. The peptidoglycan layer or cell wall isthese cells will absorb the safranin and appear red. composed of repeating disaccharides with 4 amino acidsThese are called gram-negative organisms. in a side chain extending from each disaccharide. Gram-positive = BLUE Fig. 1-2. The amino-acid chains of the peptidoglycan Im positively BLUE over you!! covalently bind to other amino acids from neighboring chains. This results in a stable cross-linked structure. Gram-negative = RED The enzyme that catalyzes the formation of this linkage No (negative) RED commies!! is called transpeptidase and is located in the inner cy- toplasmic membrane. The antibiotic penicillin binds to The different stains are the result of differences in the and inhibits this enzyme. For this reason the enzyme iscell walls of gram-positive and gram-negative bacteria. also called penicillin binding protein (see page 114). 1
  • 8. CHAPTER 1. BACTERIAL TAXONOMY Figure 1-2 plasmic membrane (unlike that of animals) has no cho- lesterol or other sterols. An important polysaccharide present in the gram- positive cell wall is teichoic acid. It acts as an antigenic determinant, so it is important for serologic identifica- tion of many gram-positive species. Fig. 1-5. The gram-negative cell envelope has S layers, not including the periplasmic space. Like gram-positiveFigure 1-3Fig. 1-3. The gram-positive cell wall is very thick and bacteria, it has 1) a cytoplasmic membrane surroundedhas extensive cross-linking of the amino-acid side by 2) a peptidoglycan layer. 3) In addition, a gram-chains. In contrast, the gram-negative cell wall is very negative cell has a unique outer cell membrane.thin with a fairly simple cross-linking pattern. The inner cytoplasmic membrane (as in gram-positive bacteria) contains a phospholipid bilayer with embed-Fig. 1-4. The gram-positive cell envelope has an outer ded proteins. Gram-negative bacteria have a periplas-cell wall composed of complex cross-linked peptidogly- mic space between the cytoplasmic membrane and ancan, teichoic acid, polysaccharides, and other proteins. extremely thin peptidoglycan layer. This periplasmicThe inner surface of the cell wall touches the cytoplas- space is filled with a gel that contains proteins and en-mic membrane. The cytoplasmic membrane contains zymes. The thin peptidoglycan layer does not containproteins that span the lipid bilayer. The bacterial cyto- teichoic acid, although it does have a small helical Figure 1-4 2
  • 9. CHAPTER 1. BACTERIAL TAXONOMY GRAM-NEGATIVE CELL ENVELOPE OUTER MEMBRANE MUREIN LIPOPROTEIN PEPTIDOGLYCAN LAYER (CELL WALL) PERIPLASMIC SPACE CYTOPLASMIC MEMBRANE EMBEDDED PROTEINSFigure 1-5 lipoprotein called murein lipoprotein. This lipopro- tein is important because it originates from the peptido- glycan layer and extends outward to bind the unique third outer membrane. This last membrane is similar to other cell membranes in that it is composed of two lay- ers of phospholipid (bilayer) with hydrophobic tails in the center. What makes it unique is that the outermost portion of the bilayer contains lipopolysaccharide (LPS). Fig. 1-6. Lipopolysaccharide (LPS) is composed of 3 covalently linked components: 1) Outer carbohydrate chains of 1-50 oligosaccha- ride units that extend into the surrounding media. These differ from one organism to another and are anti-Figure 1-6 genic determinants. This part is called the 0-specific 3
  • 10. CHAPTER 1. BACTERIAL TAXONOMY Gram-Positive Cells Gram-Negative Cells 2 Layers: 3 Layers: 1. Inner cytoplasmic membrane 1. Inner cytoplasmic membrane 2. Outer thick peptidoglycan layer 2. Thin peptidoglycan layer (60-100% peptidoglycan) (5- 10% peptidoglycan) 3. Outer membrane with lipopolysaccharide (LPS) Low lipid content High lipid content NO endotoxin (except Listeria Endotoxin (LPS) - lipid A monocytogenes) NO periplasmic space Periplasmic space NO porin channel Porin channel Vulnerable to lysozyme and Resistant to lysozyme and penicillin attack penicillin attack Figure 1-7 DIFFERENCES BETWEEN GRAM- -POSITIVE AND GRAM-NEGATIVE ORGANISMSside chain or the 0-antigen. Think of O for Outer to dally dissolved by alcohol, thus washing out the crystalhelp remember this. violet and allowing the safranin counterstain to take. 2) The center part is a water soluble core polysac-charide. Fig. 1-7. Summary of differences between gram- positive and gram-negative bacteria. BACTERIAL MORPHOLOGY 3) Interior to the core polysaccharide is the thirdcomponent, lipid A, which is a disaccharide with mul-tiple fatty acid tails reaching into the membrane. LipidA is toxic to humans and is known as the gram-negative Bacteria have 4 major shapes:endotoxin. When bacterial cells are lysed by our effi-ciently working immune system, fragments of mem- 1) Cocci: spherical.brane containing lipid A are released into the 2) Bacilli: rods. Short bacilli are called coc-circulation, causing fever, diarrhea, and possibly fatal cobacilli.endotoxic shock (also called septic shock). 3) Spiral forms: comma-shaped, S-shaped, or spi- ral-shaped. Embedded in the gram-negative outer membrane are 4) Pleomorphic: lacking a distinct shape (like jello).porin proteins, which allow passage of nutrients. These The different shaped creatures organize together intoare also unique to gram-negative organisms. more complex patterns, such as pairs (diplococci), clus- What does this mean clinically? ters, strips, and single bacteria with flagella. The differences between gram-positive and gram- Fig. 1-8. Bacterial morphology. negative organisms result in varied interactions with SO, WHAT ARE THE NAMES?!!!! Gram-Positive the environment. The gram-positive thickly meshed peptidoglycan layer does not block diffusion of low mol- ecular weight compounds, so substances that damage the cytoplasmic membrane (such as antibiotics, dyes, Start by remembering that there are 6 classic gram- and detergents) can pass through. However, the gram- positive bugs that cause disease in humans, and basi-negative outer lipopolysaccharide-containing cell mem- cally every other organism is gram-negative.brane blocks the passage of these substances to the Of the gram-positives, 2 are cocci, and the other 4 arepeptidoglycan layer and sensitive inner cytoplasmic rod-shaped (bacilli).membrane. Therefore, antibiotics and chemicals that The 2 gram-positive cocci both have the word coccusattempt to attack the peptidoglycan cell wall (such as in their names:penicillins and lysozyme) are unable to pass through. 1) Streptococcus forms strips of cocci. Interestingly, the crystal violet stain used for Gram 2) Staphylococcus forms clusters of cocci.staining is a large dye complex that is trapped in thethick, cross-linked gram-positive cell wall, resulting in Two of the 4 gram-positive rods produce sporesthe gram-positive blue stain. The outer lipid-containing (spheres that protect a dormant bacterium from thecell membrane of the gram-negative organisms is par- harsh environment). They are: 4
  • 11. CHAPTER 1. BACTERIAL TAXONOMY Gram-Negative COCCI Of the gram-negative organisms, there is only one (looks like 2 coffee beans kissing): Neisseria. group of gram-negative cocci. It is actually a diplococcus There is also just 1 group of spiral-shaped organisms: BACILLI or RODS the Spirochetes. This group includes the bacterium Tre- ponema pallidum, which causes syphilis. The rest are gram-negative rods or pleomorphic. SPIRAL Exceptions: 1) Mycobacteria are weakly gram-positive but COMMA stain better with a special stain called the acid-fast stain (See Chapter 14). This special group includes or- ganisms that cause tuberculosis and leprosy. S-SHAPED 2) Spirochetes have a gram-negative cell wall but are too small to be seen with the light microscope and so must be visualized with a special darkfield microscope. 3) Mycoplasma do not have a cell wall. They only have a simple cell membrane, so they are neither gram- PLEOMORPHIC positive nor gram-negative. Fig. 1-9. Summary of morphological differences among the bacteria. CLUSTERS CYTOPLASMIC STRUCTURES Bacterial DNA usually consists of a single circle of STRIPS double-stranded DNA. Smaller adjacent circles of double-stranded DNA are called plasmids; they often contain antibiotic resistance genes. Ribosomes are DIPLOCOCCI composed of protein and RNA and are involved in the translation process, during the synthesis of proteins. Bacteria, which are procaryotes, have smaller ribo- somes (70S) than animals (80S), which are eucaryotes. WITH FLAGELLA Bacterial ribosomes consist of 2 subunits, a large sub- unit ( 50S) and a small subunit (30S). These numbers re- late to the rate of sedimentation. Antibiotics, such as erythromycin and tetracycline, have been developed that attack like magic bullets. They inhibit protein syn- thesis preferentially at the bacterial ribosomal subunits while leaving the animal ribosomes alone. Erythromy-Figure 1-8 cin works at the 50S subunit, while tetracycline blocks protein synthesis at the 30S subunit. 3) Bacillus 4) Clostridium METABOLIC CHARACTERISTICS The last 2 gram-positive rods do not form spores: Bacteria can be divided into groups based on their metabolic properties. Two important properties include: 5) Corynebacterium 1) how the organism deals with oxygen, and 2) what the 6) Listeria, which surprisingly has endotoxin-sur- organism uses as a carbon and energy source. Otherprising because ALL other organisms with endotoxin properties include the different metabolic end-productsare gram-negative. that bacteria produce such as acid and gas. 5
  • 12. CHAPTER 1. BACTERIAL TAXONOMY MORPHOLOGY GRAM-POSITIVE GRAM-NEGATIVE Circular (Coccus) Streptococcus Neisseria Staphylococcus Rod (Bacillus) Corynebacterium ENTERICS (live in the GI tract): Listeria Escherichia coli Bacillus Shigella Clostridium Salmonella • Yersinia Klebsiella Proteus Enterobacter Mycobacterium (acid-fast) Serratia Vibrio Campylobacter Helicobacter Pseudomonas BacteroIdes (anaerobic) Haemophilus Bordetella Legionella Yersinia Francisella Brucella Pasteurella Gardnerella Spiral Spirochetes: Treponema Borrelia Leptospira Branching filamentous growth Actinomyces (anaerobic) (like fungi) Nocardia (partially acid-fast) Pleomorphic Chlamydia Rickettsiae No cell wall MycoplasmaFigure 1-9 MORPHOLOGICAL DIFFERENCES AMONG THE BACTERIAOxygen 3) Superoxide dismutase breaks down the super- oxide radical in the following reaction: How bacteria deal with oxygen is a major factor intheir classification. Molecular oxygen is very reactive,and when it snatches up electrons, it can form hydrogenperoxide (H2O2), superoxide radicals (02i, and a hy- Bacteria are classified on a continuum. At one end aredroxyl radical (OH - ). All of these are toxic unless bro- those that love oxygen, have all the preceding protectiveken down. In fact, our very own macrophages produce enzymes, and cannot live without oxygen. On the oppo-these oxygen radicals to pour over bacteria. There are 3 site end are bacteria which have no enzymes and prettyenzymes that some bacteria possess to break down much kick the bucket in the presence of oxygen:these oxygen products: 1) Obligate aerobes: These critters are just like us in that they use glycolysis, the Krebs TCA cycle, and the 1) Catalase breaks down hydrogen peroxide in the electron transport chain with oxygen as the final elec-following reaction: tron acceptor. These guys have all the above enzymes. 2) Facultative anaerobes: Dont let this name fool you! These bacteria are aerobic. They use oxygen as an 2) Peroxidase also breaks down hydrogen peroxide. electron acceptor in their electron transfer chain and 6
  • 13. CHAPTER 1. BACTERIAL TAXONOMY OBLIGATE FACULTATIVE MICROAEROPHILIC OBLIGATE AEROBES ANAEROBES ANAEROBES Gram-positive Nocardia Staphylococcus Streptococcus Clostridium (weakly acid-fast) Bacillus anthracis Bacillus cereus Corynebacterium Listeria Actinomyces Gram-negative Neisseria Most other gram- Spirochetes Bacteroides Pseudomonas negative rods Treponema Bordetella Borrelia Legionella Leptospira Brucella Campylobacter Acid-fast Mycobacterium Nocardia No cell wall Mycoplasma *Chlamydiaand Rickettsia do not have the metabolic machinery to utilize oxygen. They are energy parasites, and must steal their hosts ATP.Figure 1-10 OXYGEN SPECTRUMhave catalase and superoxide dismutase. The only dif- erotrophs. All the medically important bacteria areference is that they can grow in the absence of oxygen chemoheterotrophs because they use chemical andby using fermentation for energy. Thus they have the organic compounds, such as glucose, for energy.faculty to be anaerobic but prefer aerobic conditions. Fermentation (glycolysis) is used by many bacteriaPhis is similar to the switch to anaerobic glycolysis that for oxygen metabolism. In fermentation, glucose is bro-human muscle cells undergo during sprinting. ken down to pyruvic acid, yielding ATP directly. There 3) Microaerophilic bacteria (also called aero- are different pathways for the breakdown of glucose totolerant anaerobes): These bacteria use fermentation pyruvate, but the most common is the Embden-and have no electron transport system. They can toler- Meyerhof pathway. This is the pathway of glycolysisate low amounts of oxygen because they have superox- that we have all studied in biochemistry. Following fer-ide dismutase (but they have no catalase). mentation the pyruvate must be broken down, and the 4) Obligate anaerobes: These guys hate oxygen different end products formed in this process can beand have no enzymes to defend against it. When you are used to classify bacteria. Lactic acid, ethanol, propionicworking on the hospital ward, you will often draw blood acid, butyric acid, acetone, and other mixed acids canfor culture. You will put the blood into 2 bottles for be formed.growth. One of these is an anaerobic growth media with Respiration is used with the aerobic and facultativeno oxygen in it! anaerobic organisms. Respiration includes glycolysis, Krebs tricarboxylic-acid cycle, and the electron trans-Fig. 1-10. The oxygen spectrum of the major bacterial port chain coupled with oxidative phosphorylation.groups. These pathways combine to produce ATP.Carbon and Energy Source Obligate intracellular organisms are not capable of the metabolic pathways for ATP synthesis and thus Some organisms use light as an energy source (pho- must steal ATP from their host. These bacteria live intotrophs), and some use chemical compounds as an en- their host cell and cannot survive without the host.ergy source (chemotrophs). Of the organisms that use Further metabolic differences (such as sugar sourceschemical sources, those that use inorganic sources, such used, end products formed, and the specific need for cer-as ammonium and sulfide, are called autotrophs. Oth- tain nutrients) figure in classifying bacteria and will beers use organic carbon sources and are called het- discussed in the chapters covering specific organisms.
  • 14. CHAPTER 2. CELL STRUCTURES, VIRULENCE FACTORS AND TOXINS Figure 2-1Virulent organisms are those that can cause disease. gradient or away from the gradient. This movement isThe virulence of an organism is the degree of organism called chemotaxis.pathogenicity. Virulence depends on the presence of cer-tain cell structures and on bacterial exotoxins and en- Fig. 2-2. Bacteria can have a single polar flagellumdotoxins, all of which are virulence factors. ( polar means at one end of the cell) as is the case with Vibrio cholera, or many peritrichous flagella (all CELL STRUCTURES AS VIRULENCE around the cell) as is the case with Escherichia coli and FACTORS Proteus mirabilis. Shigella does not have flagella.Flagella Pili Pili (also called fimbriae) are straight filamentsFig. 2-1. Flagella are protein filaments that extend arising from the bacterial cell wall, making the bac-like long tails from the cell membranes of certain gram- terium look like a porcupine.positive and gram-negative bacteria. These tails, whichare several times the length of the bacterial cell, move Fig. 2-3. Pili are much shorter than flagella and dothe bacteria around. The flagellum is affixed to the bac- not move. Pili can serve as adherence factors (in whichteria by a basal body. The basal body spans through case they are called adhesins). Many bacteria possessthe entire cell wall, binding to the inner and outer cell adhesins that are vital to their ability to cause disease.membrane in gram-negative bacteria and to the inner For example, Neisseria gonorrhea has pili that allow itmembrane in gram-positive bugs (the gram-positive to bind to cervical cells and buccal cells to cause gonor-bacteria dont have an outer membrane). The basal body rhea. Escherichia coli and Campylobacter jejuni cannotspins around and spins the flagellum. This causes the cause diarrhea without their adhesins to bind to the in-bacterial flagella to undulate in a coordinated manner testinal epithelium, and Bordetella pertussis uses itsto move the bacteria toward a chemical concentration adhesin to bind to ciliated respiratory cells and cause 8
  • 15. CHAPTER 2. CELL STRUCTURES, VIRULENCE FACTORS AND TOXINS whooping cough. Bacteria that do not produce these pili cannot grab hold of their victim; they lose their viru- lence and thus cannot infect humans. There are also special pili, discussed in the next chapter, called sex pili. Capsules Capsules are protective walls that surround the cell membranes of gram-positive and gram-negative bacteria. They are usually composed of simple sugar residues. Bacteria secrete these sugar moieties, which then coat their outer wall. One bacterium, Bacillus an- thracis, is unique in that its capsule is made up of amino acid residues. Fig. 2-4. Capsules enable bacteria to be more viru- lent because macrophages and neutrophils are unable to phagocytize the encapsulated buggers. For exam- ple, Streptococcus pneumoniae has a capsule. WhenFigure 2-2 grown on media, these encapsulated bacteria appear as smooth (S) colonies that cause rapid death when in- jected into mice. Some Streptococcus pneumoniae do not have capsules and appear as rough (R) colonies on agar. Figure 2-3 9
  • 16. CHAPTER 2. CELL STRUCTURES, VIRULENCE FACTORS AND TOXINSFigure 2-4These rough colonies have lost their virulence and wheninjected into mice do not cause death. Two important tests enable doctors to visualizecapsules under the microscope and aid in identifyingbacteria: 1) India ink stain: Because this stain is not takenup by the capsule, the capsule appears as a transparenthalo around the cell. This test is used primarily to iden-tify the fungus Cryptococcus. 2) Quellung reaction: The bacteria are mixed withantibodies that bind to the capsule. When these anti-bodies bind, the capsule swells with water, and this canbe visualized microscopically. Figure 2-5 Antibodies directed against bacterial capsules protect that protects the individual against future infectionsus as they help our macrophages and neutrophils bind by this and eat the encapsulated bacteria. The process of an-tibodies binding to the capsule is called opsonization. EndosporesFig. 2-5. Once the antibodies have bound to the Endospores are formed by only 2 genera of bacteria,bacterial capsule (opsonization), the macrophage or both of which are gram-positive: the aerobic Bacillusneutrophil can then bind to the Fc portion of the anti- and the anaerobic Clostridium.body and gobble up the bacteria. A vaccine againstStreptococcus pneumoniae contains antigens from the Fig. 2-6. Endospores are metabolically dormant23 most common types of capsules. Immunization with forms of bacteria that are resistant to heat (boiling),this vaccine elicits an immune response against the cold, drying and chemical agents. They have a multi-capsular antigens and the production of antibodies layered protective coat consisting of: 10
  • 17. CHAPTER 2. CELL STRUCTURES, VIRULENCE FACTORS AND TOXINS phagosome-lysosome fusion, thus escaping the hosts deadly hydrogen peroxide and superoxide radicals. In- side the cells these bacteria are safe from antibodies and other immune defenses. FACULTATIVE INTRACELLULAR ORGANISMS 1. Listeria monocytogenes 2. Salmonella typhi 3. Yersinia 4. Francisella tularensis 5. Brucella 6. Legionella 7. Mycobacterium Figure 2-7 Fig. 2-7. Facultative intracellular organisms. TOXINS Exotoxins Exotoxins are proteins that are released by both gram-positive and gram-negative bacteria. They may cause many disease manifestations. Essentially, exo- toxins are released by all the major gram-positive genera except for Listeria monocytogenes, which pro- duces endotoxin. Gram-negative bacteria such as Vibrio cholera, Escherichia coli, and others can also excrete ex- otoxins. Severe diseases caused by bacterial exotoxins i nclude anthrax (Saddam Husseins threatened germ warfare agent), botulism, tetanus, and cholera. Neurotoxins are exotoxins that act on the nerves or motor endplates to cause paralysis. Tetanus toxin andFigure 2-6 botulinum toxin are examples. Enterotoxins are exotoxins that act on the gas- A) A cell membrane trointestinal (GI) tract to cause diarrhea. Enterotoxins B) A thick peptidoglycan mesh inhibit NaCl resorption, activate NaCl secretion, or kill C) Another cell membrane intestinal epithelial cells. The common end result is D) A wall of keratin-like protein the osmotic pull of fluid into the intestine, which E) An outer layer called the exosporium causes diarrhea. The enterotoxins cause 2 disease manife- stations: Spores form when there is a shortage of needed nu-trients and can lie dormant for years. Surgical instru- 1) Infectious diarrhea: Bacteria colonize and bindments are heated in an autoclave, which uses steamunder pressure, to 121°C for 15 minutes, in order to en- to the GI tract, continuously releasing their enterotox-sure the destruction of Clostridium and Bacillus spores. ins locally. The diarrhea will continue until the bacteriaWhen the spore is exposed to a favorable nutrient or en- are destroyed by the immune system or antibiotics (orvironment, it becomes active again. the patient dies secondary to dehydration). Examples: Vibrio cholera, Escherichia coli, Campylobacter jejuni, and Shigella dysenteriae.Facultative Intracellular Organisms 2) Food poisoning: Bacteria grow in food and re- lease enterotoxin in the food. The enterotoxin is in- Many bacteria are phagocytosed by the hosts gested resulting in diarrhea and vomiting for less thanmacrophages and neutrophils yet survive within these 24 hours. Examples: Bacillus cereus and Staphylococcuswhite blood cells unharmed!!! These bacteria inhibit aureus. 11
  • 18. CHAPTER 2. CELL STRUCTURES, VIRULENCE FACTORS AND TOXINS Pyrogenic exotoxins stimulate the release of cy- To better understand septic shock, let us back up andtokines and can cause rash, fever, and toxic shock syn- review some terms.drome (see page 33). Examples: Staphylococcus aureus Bacteremia: This is simply bacteria in the blood-and Streptococcus pyogenes. stream. Bacteria can be detected by isolating the of- Tissue invasive exotoxins allow bacteria to de- fending critters in blood cultures. Bacteremia can occurstroy and tunnel through tissues. These include en- silently and without symptoms. Brushing your teeth re-zymes that destroy DNA, collagen, fibrin, NAD, red sults in transient bacteremia with few systemic conse-blood cells, and white blood cells. quences. Bacteremia can also trigger the immune Miscellaneous exotoxins, which are the principle system, resulting in sepsis and possibly death.virulence factors for many bacteria, can cause disease Sepsis: Sepsis refers to bacteremia that causes a sys-unique to the individual bacterium. Often the exact role temic immune response to the infection. This responseof the exotoxin is poorly understood. can include high or low temperature, elevation of the white blood cell count, and fast heart rate or breathing Fig. 2-S. This chart gives many of the important exo- rate. Septic patients are described as "looking sick." toxins and compares their mechanisms of action. Glance Septic shock: Sepsis that results in dangerous dropsover the chart now and return to it as you study indi- i n blood pressure and organ dysfunction is called septicvidual bacteria. shock. It is also referred to as endotoxic shock be-Fig. 2-9. Exotoxin subunits in Bacillus anthracis, cause endotoxin often triggers the immune responseClostridium botulinum, Clostridium tetani, Corynebac- that results in sepsis and shock. Since gram-positiveterium diphtheriae, and Vibrio cholera. Their exotoxins bacteria and fungi can also trigger this adverse immuneare all composed of 2 polypeptide subunits bound to- response, the term septic shock is more appropriategether by disulfide bridges. One of these subunits and inclusive.(called B for binding or H for holding on) binds to the The chain of events that lead to sepsis and oftentarget cell. The other subunit (called A for action or L death begins with a localized site of infection of gram-for laser) then enters the cell and exerts the toxic effect. negative or gram-positive bacteria or fungi. From thisPicture these subunits as a key (B and H) and a gun (A site or from the blood (bacteremia), the organisms re-and L) bound together by disulfide bonds. The key opens lease structural components (such as endotoxin and/orthe cell, and then the gun does its damage. exotoxin) that circulate in the bloodstream and stimu- late immune cells such as macrophages and neu-Endotoxins trophils. These cells, in response to the stimulus, release a host of proteins that are referred to as en- Remember from the last chapter that endotoxin is dogenous mediators of sepsis.lipid A, which is a piece of the outer membrane The most famous endogenous mediator of sepsis islipopolysaccharide (LPS) of gram-negative bacteria (see tumor necrosis factor (TNF). TNF is also calledFig. 1-6). Lipid A/endotoxin is very toxic and is released cachectin because it is released from tumors, produc-when the bacterial cell undergoes lysis (destruction). ing a wasting (weight loss) syndrome, called cachexia,Endotoxin is also shed in steady amounts from living in cancer patients. Injecting TNF into experimentalbacteria. Sometimes, treating a patient who has a gram- animals produces hypotension and death (septic shock).negative infection with antibiotics can worsen the pa- In sepsis, TNF triggers the release of the cytokinetients condition because all the bacteria are lysed, interleukin-1 from macrophages and endothelial cells,releasing large quantities of endotoxin. Endotoxin dif- which in turn triggers the release of other cytokinesfers from exotoxin in that it is not a protein ex- and prostaglandins. This churning maelstrom of medi-creted from cells, but rather is a normal part of ators at first defends the body against the offendingthe outer membrane that sort of sheds off, espe- microorganisms, but ultimately turns against the body.cially during lysis. Endotoxin is ONLY present in The mediators act on the blood vessels and organsgram-negative bacteria with one exception: Listeria to produce vasodilatation, hypotension, and organ sys-monocytogenes, a gram-positive bacteria, has endotoxin. tem dysfunction. The mortality rate for septic shock is high: up to 40%Septic Shock of patients will die, even with intensive care and an- tibiotic therapy. For every organ system that fails the Septic shock (endotoxic shock) is a common and mortality rises. Usually two organs are involved (vas-deadly response to both gram-negative and gram- cular system with hypotension and lungs with hypoxia)positive infection. In fact, septic shock is the number and the mortality rate is about 40%. For each addi-one cause of death in intensive care units and the 13th tional organ failure (renal failure, etc.) add 15-20%most common cause of death in the U.S. (Parrillo, 1990). mortality! 12
  • 19. Figure 2-8 EXOTOXINS
  • 20. Figure 2-8 (continued) M. Gladwin and B. Trattler, Clinical Microbiology Made Ridiculously Simple ©MedMaster
  • 21. CHAPTER 2. CELL STRUCTURES, VIRULENCE FACTORS AND TOXINS Figure 2-9 ORGAN SYSTEM EFFECT ON ORGAN SYSTEM DAMAGING EFFECT ON BODY Vascular system Vasodilation 1. Decreased blood pressure 2. Organ hypoperfusion Heart Myocardial depression 1. Decreased cardiac output 2. Decreased blood pressure 3. Organ hypoperfusion Kidneys Acute renal failure 1. Decreased urine output 2. Volume overload 3. Accumulation of toxins Lungs Adult respiratory distress syndrome Hypoxia Liver Hepatic failure 1. Accumulation of metabolic toxins 2. Hepatic encephalopathy Brain Encephalopathy A lteration in mental status Coagulation system Disseminated intravascular coagulation 1. Clotting 2. Bleeding Figure 2-10 EFFECTS OF SEPTIC SHOCKTreatment host of other investigational agents (tumor necrosis factor soluble receptor, nitric oxide antagonists, and The most important principle of treatment is to find antioxidant compounds), have met with disappointing the site of infection and the bug responsible and eradi- results. Most of these treatments have failed to reduce cate it! The lung is the most common site (pneumonia) mortality in clinical trials. followed by the abdomen and urinary tract. In one-third of cases a site of infection is not identified. Antibiotic therapy is critical with a 10 to 15 fold increased mortal- Fig. 2-10. The end organ effects of septic shock. ity when antibiotics are delayed. Even while working up the site of infection you should start broad coverage an- References tibiotics (called empiric therapy). In other words, as soon as the patient looks sick, start blasting your shotgun at Parrillo JE. Pathogenic mechanisms of septic shock. N Engl J all potential targets. Fire early and hit everything. Med 1993;328:1471-1477. Blood pressure must be supported with fluids and Parrillo JE, moderator. Septic shock in humans: advances indrugs (dopamine and norepinephrine are commonly the understanding of pathogenesis, cardiovascular dys-used) and oxygenation maintained (intubation and me- function, and therapy. Ann Intern Med 1990;113:227-42.chanical ventilation is often required). In the last decades, efforts to block the inflammatory Recommended Review Article:cascade with monoclonal antibodies against endotoxin,tumor necrosis factor, and interleukin-1, anti-inflam- Wheeler, AP, Bernard GR. Treating patients with septicmatory agents such as ibuprofen and steroids, and a shock. N Engl J Med 1999;340:207-214. 15
  • 22. insertions CHAPTER 3. BACTERIAL SEX GENETICSThe bacterial chromosome is a double-stranded DNA in their cellular capsule. Griffith used smooth encapsu- molecule that is closed in a giant loop. Because there is l ated pneumococci, which cause violent infection andonly one copy of this molecule per cell, bacteria exist in death in mice, and rough nonencapsulated pneumo- a haploid state. Bacteria do not have nuclear mem- cocci, which do not kill mice. You can think of the en-branes surrounding their DNA. capsulated pneumococci as smooth hit men who kill This chapter does not attempt to cover all the details mice, and the rough nonencapsulated pneumococci asof bacterial genetics, such as replication, transcription, only acting rough (they are pushovers and cant kill aand translation. These topics are covered extensively in flea). Griffith heat-killed the smooth encapsulated badgenetics courses. Instead, this chapter covers the mech- guys and injected them, along with the live roughanisms of bacterial exchange of genetic information. nonencapsulated pushovers, into mice. Lo and behold,You see, procaryotes have it rough as they do not engage the mice died, and when he cultured out bacteria fromi n sexual union with other bacteria. They undergo gene the blood, he could only find live smooth encapsulatedreplication, forming an exact copy of their genome, and pneumococci. The gene encoding the capsule had beenthen split in two, taking a copy with each half (binary released from the heat-killed bacteria and became in-fission). The cells of higher organisms (eucaryotes) con- corporated into the living rough nonencapsulated bac-tribute a set of gametes from each parent and thus en- teria. The rough bacteria were thus transformed intosure genetic diversity. So how do the sexless creatures virulent encapsulated smooth bacteria.undergo the genetic change so necessary for survival? Scientists now use this method extensively for in- One mechanism is simple mutation. However, it is serting recombinant DNA and for mapping genes on rare for a single point mutation to change an organism chromosomes. It can be used in mapping because thei n a helpful manner. Point mutations usually result in frequency of transformation leading to two traits beingnonsense or missense (does this make sense?). There transferred is relative to their distance apart on theare 4 ways in which bacteria are able to exchange ge- genome. The closer they are to each other, the morenetic fragments: 1) transformation, 2) transduction, 3) likely that they will be transferred together.conjugation (so much for celibacy), and 4) transposon . TRANSDUCTION CHANGE = SURVIVAL Transduction occurs when a virus that infects bacte- The exchange of genetic material allows for the shar- ria, called a bacteriophage, carries a piece of bacter-i ng of genes that code for proteins, such as those that ial DNA from one bacterium to another. To understandprovide antibiotic resistance, exotoxins, enzymes, and this topic, let us digress for a moment and talk aboutother virulence factors (pili, flagella, and capsules). bacteriophages.Scientists can take advantage of these exchange mech-anisms for genetic engineering and chromosomal map- Fig. 3-1. Bacteriophages resemble most viruses inping. Read on ... but only if you are over 21 years old. having a protein coat called a capsid that surrounds a molecule of DNA or RNA. They look almost like spiders with long skinny necks. TRANSFORMATION The phage will bind by its tail fibers to specific recep- Naked DNA fragments from one bacterium, released tors on the bacterial cell surface. This is called adsorp-during cell lysis, bind to the cell wall of another bac- tion. The phage then undergoes penetration. Muchterium. The recipient bacterium must be competent, like a spider squatting down and sinking in its stinger,which means that it has structures on its cell wall that the phage pushes the long hollow tube under its neckcan bind the DNA and take it up intracellularly. Recip- sheath through the bacterial cell wall and cytoplasmici ent competent bacteria are usually of the same species membrane. DNA in the head is injected through theas the donor. The DNA that has been brought in can tube into the bacterium.then incorporate itself into the recipients genome ifthere is enough homology between strands (another Fig. 3-2. Following adsorption and penetration, thereason why this transfer can only occur between closely i njected DNA takes over the host bacterias RNA poly-related bacteria). merase for the transcription of phage DNA to mesenger The famous example of this type of exchange is the ex- RNA (mRNA). New capsids, DNA, and enzymes areperiment conducted by Frederick Griffith in 1928. He formed, and the bacterial cell fills with new phages. Atused the Streptococcus pneumoniae bacteria, which are some point the cell can hold no more particles and lyses,classified into many different types based on differences releasing the phages. 16
  • 23. CHAPTER 3. BACTERIAL GENETICS Figure 3-1 To make things more complicated, there are two types of phages, virulent phages and temperate phages. Virulent phages behave as shown in Fig. 3-2, infecting the bacteria, reproducing, and then lysing and killing the bacteria. On the other hand, temperate phages have a good temperament and do not immediately lyse the bacteria they infect. The temperate phage undergoes ad- sorption and penetration like the virulent phage but then, rather than undergoing transcription, its DNA be- comes incorporated into the bacterial chromosome. The DNA then waits for a command to activate. Fig. 3-3. The integrated temperate phage genome is called a prophage. Bacteria that have a prophage integrated into their chromosome are called lysogenic because at some time the repressed prophage can be- come activated. Once activated, the prophage initiates the production of new phages, beginning a cycle that ends with bacterial cell lysis. So temperate phages, although of good temperament, are like little genetic time bombs. Lysogenic immunity is the term used to describe the ability of an integrated bacteriophage (prophage) to Figure 3-2 block a subsequent infection by a similar phage. The first temperate phage to infect a bacteria produces a re- pressor protein. This "survival of the fittest" adaptation terium to another. This process is called transduction. ensures that the first temperate phage is the bacterias Just as there are two types of phages, there are two sole occupant. types of transduction. Virulent phages are involved in Now that we understand bacteriophages, lets discuss generalized transduction and temperate phages in how these phages can carry bacterial DNA from one bac- specialized transduction. 17
  • 24. CHAPTER 3. BACTERIAL GENETICS BACTERIAL DNA DISRUPTED REPLICATED BACTERIAL PHAGE DNA DNAFigure 3-3 MISPACKAGED PHAGE DNA BACTERIAL DNAGeneralized Transduction Generalized transduction occurs as follows. Afterphage penetration into a host bacterium, the phageDNA is transcribed, replicated, and translated intocapsids and enzymes. At this same time the bacterialDNA is repressed and eventually destroyed. Some-times pieces of the bacterial DNA are left intact. Ifthese pieces are the same size as the phage DNA, theycan accidentally be packed into the phage capsid head.Following lysis of the cell and release of the phages, theone phage with bacterial DNA in its head can then in-fect another bacterium. It will inject the piece of bacte-rial DNA that it is "accidentally" carrying. If there issome homology between the newly injected strand andthe recipient bacterial genome, the piece may become PHAGE WITH BACTERIAL DNAincorporated. The gene on that piece could encode aprotein that the recipient did not originally have, suchas a protein that inactivates an antibiotic. In general- Figure 3-4ized transduction, the bacteriophage is only carryingbacterial DNA, so the recipient cell will survive (since Specialized Transductionno viral genes that encode for replication and lysis are Specialized transduction occurs with temperatepresent). This type of genetic transfer is more effective phages. Remember that the temperate phage pene-than transformation because the transferred DNA trates, and then its DNA becomes incorporated into thepiece is protected from destruction during transfer by bacterial chromosome. It is then called a prophage, andthe phage capsid that holds it. the bacterium is now lysogenic ( Fig. 3-3). Normally the prophage just waits doing nothing, but it can eventuallyFig. 3-4. Generalized transduction become active. If it becomes active, the prophage DNA A) Adsorption and penetration occur. The viral DNA is spliced out of the bacterial chromosome and is thenis drawn as a thin line, and the bacterial circular DNA replicated, translated, and packaged into a drawn as a thick circle. Sometimes there is an error in splicing, and a piece of B) Destruction of the bacterial DNA leaves some in- bacterial DNA that lies at one side of the prophage willtact (thick) pieces. The phage DNA has undergone be cut, replicated, and packaged with the phage DNA.replication. This may result in a transfer of that piece of bacterial C) Capsids are translated and packed. The middle DNA to another has been packed with a bacterial DNA fragment. D) Cell lysis occurs, liberating phages including the Fig. 3-5. Specialized transduction occurs withphage with bacterial DNA. phage lambda in Escherichia coli. The site of insertion 18
  • 25. CHAPTER 3. BACTERIAL GENETICSFigure 3-5 of the lambda prophage lies between the Escherichia Fig. 3-6. The self-transmissible plasmid (F plasmid)coli gene for biotin synthesis and galactose synthesis. If has a gene that encodes enzymes and proteins that form a splicing error occurs, the biotin (BIO) gene or the the sex penis, that is, sex pilus.galactose (GAL) gene (but not both, as the piece of DNA This long protein structure protrudes from the cellspliced is of a set length) will be carried with the phage surface of the donor F(+) bacterium and binds to andDNA and packaged. Thus the gene for biotin synthesis penetrates the cell membrane of the recipient bacteriumcan now be transferred to another bacteria that does not (this is finally getting juicy!). Now that a conjugal bridgehave that capability. You will frequently hear about this has formed, a nuclease breaks off one strand of the Fform of gene acquisition; it is called lysogenic conver- plasmid DNA, and this single strand of DNA passession. For example, the gene for Corynebacterium diph- through the sex pilus (conjugal bridge) to the recipienttherias exotoxin is obtained by lysogenic conversion. bacterium. CONJUGATION Conjugation is bacterial sex at its best: hot and heavy!In conjugation DNA is transferred directly by cell-to-cellcontact, resulting in an extremely efficient exchange ofgenetic information. The exchange can occur betweenunrelated bacteria and is the major mechanism fortransfer of antibiotic resistance. For conjugation to occur, one bacterium must have aself-transmissible plasmid, also called an F plasmid(for fertility, not the other word!). Plasmids are circulardouble-stranded DNA molecules that lie outside thechromosome and can carry many genes, including thosefor drug resistance. F plasmids encode the enzymes andproteins necessary to carry out the process of conjuga-tion. Bacteria that carry F plasmids are called F(+)cells. In conjugation, an F(+) donor cell will pass its Fplasmid to an F( -) recipient cell, thus making the re-cipient F(+). Figure 3-6 19
  • 26. CHAPTER 3. BACTERIAL GENETICS As one DNA strand is passed through theconjugal bridge, the remaining strand is paired withFig. nucleotide bases (dotted line). The same thing hap-pens to the strand that passes to the other cell. At theend of the sexual union, the conjugal bridge breaksdown and both bacteria have double-stranded circular Fplasmids. The recipient F(-) cell is now F(+). Rarely, the extra-chromosomal F plasmidbecomes integrated in the neighboring bacterial chro-Fig. 3-8.mosome much in the same way as a temperate bacte-riophage does. The bacterial cell is then called a Hfrcell (High frequency of chromosomal recombinants).This integration can result in two unique mechanismsof DNA transfer: 1) The F plasmid that is now together with the entirebacterial circular DNA undergoes normal conjugation Figure 3-8 with an F( -) cell. The entire bacterial chromosome (in- cluding the integrated F plasmid) will transfer from the Hfr cell to the recipient cell. 2) The integrated F plasmid in the Hfr cell may be excised at a different site from that of integration. This can result in an F plasmid that now also contains a seg- ment of chromosomal DNA. These plasmids are called F (F prime) plasmids. This F conjugation is analo- gous to specialized transduction because in both situa- tions a nearby segment of chromosomal DNA is picked up "accidentally" and can be transferred to other bacte- rial cells. Some plasmids are non-self-transmissible plasmids. These plasmids do not have the genes necessary for di- recting conjugation. They do replicate within their host bacterium, however, and continue to be passed on as the bacteria divide in binary fission. Plasmids are tremendously important medically. Certain plasmids encode enzymes that degrade antibi- otics (penicillinase), or generate virulence factors (suchFigure 3-7 as fimbriae and exotoxins). 20
  • 27. CHAPTER 3. BACTERIAL GENETICS TRANSPOSONSFig. 3.9. Transposons are mobile genetic elements.You can visualize them as DNA pieces with legs.These pieces of DNA can insert themselves into a donorchromosome without having DNA homology. Theycan carry genes for antibiotic resistance and viru-lence factors. Transposons insert into the DNA of phages, plas-mids, and bacterial chromosomes. They do not repli-cate independently but are copied during their hostsDNA transcription. When transposons leave the DNA Figure 3-9they are incorporated in, there is frequently aberrantexcision and the transposon can carry new DNA away drug resistance can move to the plasmids of differentto another site. The importance of transposons clivi- bacterial genera, resulting in the rapid spread of resis-cally is that a transposon gene that confers a particular taut strains.
  • 28. GRAM-POSITIVE BACTERIA CHAPTER 4. STREPTOCOCCITests for Strep and Staph Streptoccal Classification Streptococci and staphylococci are both gram-positive Certain species of streptococci can either completelyspheres (cocci) and are responsible for a wide variety of or partially hemolyze red blood cells (RBCs). The strep-clinical diseases. It is often necessary to differentiate tococci are divided into three groups based on their spe-between these two organisms to prescribe the appropri- cific hemolytic ability. The streptococci are incubatedate antibiotic. The first way to differentiate them is to overnight on a blood agar plate. Beta-hemolytic strep-examine their appearance on a Gram stain. Streptococci tococci completely lyse the RBCs, leaving a clear zone ofline up one after the other like a strip of button candy, hemolysis around the colony. Alpha-hemolytic strep-while staphylococci appear as a cluster that can be vi- tococci only partially lyse the RBCs, leaving a greenishsualized as a cluster of hospital staff members posing discoloration of the culture medium surrounding thefor a group shot ( Fig. 4-1). colony. This discolored area contains unlysed RBCs and a green-colored metabolite of hemoglobin. Gamma-Fig. 4-1. A second method to differentiate streptococci hemolytic streptococci are unable to hemolyze thefrom staphylococci involves the enzyme catalase. A RBCs, and therefore we should really not use the wordquick look at our staff (Staph) picture reveals that a "hemolytic" in this situation (the term non-hemolyticCAT has joined them, so the staff picture is CAT(alase) streptococci is often used to avoid confusion).positive. That is, staphylococci possess the enzyme The streptococci can also be classified based on thecatalase, whereas streptococci do not. Staphylococci antigenic characteristics of the C carbohydrate (a car-are thus referred to as catalase positive while strepto- bohydrate found on the cell wall). These antigens arecocci are catalase negative. Catalase converts H2O2 called Lancefield antigens and are given letter names(hydrogen peroxide, which is used by macrophages ( from A, B, C, D, E, through S). Historically, theand neutrophils) into 1120 and 0 2 . To test for catalase, Lancefield antigens have been used as a major waya wire loop is rubbed across a colony of gram-positive of differentiating the many streptococci. However,cocci and mixed on a slide with 11202. If bubbles appear, there are so many different types of streptococcithe enzyme catalase must be present, and so staphylo- that we now rely less on the Lancefield antigenscocci are present. (See Fig. 5-2). and more on a combination of tests such as the above mentioned patterns of hemolysis, antigenic composition (including Lancefield), biochemical re- actions, growth characteristics, and genetic stud- ies. Although there are more than 30 species of streptococci, only 5 are significant human pathogens. Three of these pathogens have Lancefield antigens: Lancefeld group A, B and D. The other two pathogenic species of the streptococcal genus do not have Lancefield antigens, and are therefore just called by their species names: One is Streptococcus pneumoniae and the other is actually a big group of streptococci collec- tively called the Viridans group streptococci. GROUP A BETA-HEMOLYTIC STREPTOCOCCI (also called Streptococcus pyogenes) These organisms are so-named because they possess the Lancefeld group A antigen and are beta-hemolytic on blood agar. They are also called Streptococcus pyo-Figure 4-1 genes ( which means pus-producing) and cause the dis- 22
  • 29. CHAPTER 4. STREPTOCOCCI eases "strep throat," scarlet fever, rheumatic fever, and 2) Streptococcal skin infections post-streptococcal glomerulonephritis. 3) Scarlet fever The components of the streptococcal cell wall that are 4) Streptococcal toxic shock syndrome antigenic include: Beta-hemolytic group A streptococci can also cause 2 1) C carbohydrate: The C carbohydrate was used by delayed antibody mediated diseases: Rebecca Lancefield to divide streptococci into groups. Streptococcus pyogenes has the "Lancefield Group A" type 1) Rheumatic fever of C carbohydrate. 2) Glomerulonephritis 2) M protein (80 types): This is a major virulence fac- tor for the group A streptococcus. It inhibits the activation Local Invasion/Exotoxin Release of complement and protects the organism from phagocyto- sis. However, it is also the weakest point in the organisms 1) Streptococcal pharyngitis: This is the classic defense, because plasma (B) cells generate antibodies strep throat with red swollen tonsils and pharynx, a pu- against the M protein. These antibodies bind to the M pro- rulent exudate on the tonsils, high temperature, and tein (opsonization), aiding in the destruction of the organ- swollen lymph nodes. It usually lasts 5 days (penicillin ism by macrophages and neutrophils. therapy speeds recovery). Beta-hemolytic group A streptococci also have many en- "Mom, my throat hurts!!!"zymes that contribute to their pathogenicity: 2) Skin infections: Skin infections can range from folliculitis (infections of the hair follicles), cellulitis (a 1) Streptolysin O: The O stands for oxygen labile as it deep infection of the skin cells, producing red, swollenis inactivated by oxygen. This enzyme destroys red and skin which is hot to the touch), and impetigo (a vesicu-white blood cells and is the reason for the beta-hemolytic lar, blistered, eruption, most common in children, thatgroup A streptococcis beta-hemolytic ability. This enzyme becomes crusty and flaky and is frequently foundis also antigenic. Following pharyngeal or systemic beta- around the mouth). These skin infections can also behemolytic group A streptococcal infection, anti-strep- caused by Staphylococcus aureus. Therefore, treatmenttolysin O (ASO) antibodies develop. On the wards you may for these infections consists of a penicillinase resistantorder ASO titers on a patients blood to confirm recent in- penicillin like dicloxacillin, which covers both group Afection. beta-hemolytic streptococci and Staphylococcus aureus. 2) Streptolysin S_: The S stands for oxygen stabile. "Mom, my throat hurts and my skin is disinte- This is also responsible for beta-hemolysis but is not anti- grating!!!!" genic. Necrotizing Fasciitis ("Flesh-eating Streptococ- 3) Pyrogenic exotoxin (also called erythrogenic cus"): This type of group A beta-hemolytic streptococcal toxin): This is found in only a few strains of beta- infection has actually been around for years but may in- hemolytic group A streptococci, but when these strains in- deed be on the rise (news coverage certainly is). Certain vade they can cause scarlet fever. strains have M proteins that block phagocytosis, allow- ing the bacteria to move rapidly through tissue. Strep- Some strains produce pyrogenic exotoxins that are su- tococci enter through a break in the skin caused by perantigens. The exotoxins directly superstimulate T cells trauma and then follow a path along the fascia which to pour out inflammatory cytokines. This causes a strepto- lies between the subcutaneous tissue and muscle.coccal toxic shock syndrome (Holm, 1996). More on scarlet Within a day the patient develops swelling, heat, andfever and toxic shock syndrome later. . . redness that moves rapidly from the initial skin infec- 4) Other enzymes include streptokinase (activates tion site. A day later the skin color changes from red tothe proteolytic enzyme plasmin, which breaks up fibrin purple to blue, and large blisters (bullae) form. Laterblood clots), hyaluronidase, DNAases, anti-C5a pepti- the skin dies and muscle may also become infecteddase, and others (see Fig. 2-S). (myositis). Staphylococcus aureus has many enzymes that are sim- This infection must be recognized early and the fas-ilar to those of streptococci. You will learn about these in cia surgically removed. Rapid antibiotic therapy is cru-the next chapter. cial. Group A beta-hemolytic streptococci are still exquisitely sensitive to penicillin G. It may be wise to Beta-hemolytic group A streptococci cause 4 types of dis- add clindamycin, as this drug rapidly shuts down strep-ease by local invasion and/or exotoxin release. These tococcal metabolism and will block toxin productioninclude: ( Holm, 1996; Stevens, 1988). Even with antibiotics and 1) Streptococcal pharyngitis surgery the mortality rate is high (> 50%). 23
  • 30. CHAPTER 4. STREPTOCOCCI Figure 4-3Figure 4-2 NOT after a skin infection). The 6 major manifestations of rheumatic fever are: a) Fever. Necrotizing fasciitis can also be caused by Staphylo- b) Myocarditis (heart inflammation).coccus, Clostridium species, gram-negative enterics, or c) Joint swelling (arthritis).mixed infection with more than one of these bacteria d) Chorea (uncontrolled dance-like movements of the( Stevens, 1992). extremities) which usually begins 2-3 weeks after the 3) Scarlet fever: Certain beta-hemolytic group A pharyngitis.streptococci not only cause a sore throat, but also pro- e) Subcutaneous nodules (rubbery nodules just un-duce an exotoxin called either pyrogenic toxin or ery- der the skin).throgenic toxin. This exotoxin is acquired by lysogenic f) Rash, called erythema marginatum because itconversion (see Chapter 3). The exotoxin produces fever has a red margin that spreads out from its center.(so it is pyrogenic) and causes a scarlet-red rash. The Fig. 4-3. Picture John Travolta in the movierash begins on the trunk and neck, and then spreads to Rheumatic Fever, the upcoming sequel to Saturdaythe extremities, sparing the face. The skin may peel off Night Fever. His heart is damaged from the stress ofin fine scales during healing. the hours of disco dancing, his joints are aching from "Mom, my body is turning scarlet!!!!" dropping to his knees, and his arms are moving rhyth- mically in a disco choreiform jam.Fig. 4-2. "MOM, help!!!" Pharyngitis, impetigo, and Rheumatic fever is antibody-mediated. There are anti-scarlet fever. Note that scarlet fever actually spares gens in the heart that are similar to the antigens of thethe face. beta-hemolytic group A streptococci. Therefore, the anti- 4) Streptococcal toxic shock syndrome: It is now bodies that form to eradicate this particular streptococcus also cross-react with antigens in the heart. This immuno-clear that beta-hemolytic group A streptococci can cause logic attack on the heart tissue causes heart inflamma-toxic shock syndrome like that caused by Staphylococ- tion, called myocarditis. Patients may complain of chestcus aureus. Similar to scarlet fever, streptococcal toxicshock syndrome is also mediated by the release of pyro- pain and may develop arrhythmias or heart failure.genic toxin. See Chapter 5 and Fig. 5-9 for more details. Over years, likely after recurrent infections with streptococci, the heart becomes permanently damaged.Consider adding clindamycin to penicillin G, as the for- The most frequently damaged site of the heart is the mi-mer rapidly shuts down streptococcal metabolism and tral valve, followed by the aortic valve. These damagedtoxin production (Stevens, 1988; Holm, 1996). valves may become apparent many years (10-20) after the initial myocarditis, and can be picked up on physi-Delayed Antibody-Mediated Disease cal exam because they produce heart murmurs. So, 1) Rheumatic fever: there is an initial myocarditis, and many years later rheumatic valvular heart disease develops. With the advent of penicillin, rheumatic fever is now These patients are susceptible to recurrent boutsuncommon. It usually strikes children 5-15 years of age. of rheumatic fever and further heart damage. To pre-When it occurs, it has been shown to follow untreated vent further damage to the heart (which is permanentbeta-hemolytic group A streptococcal pharyngitis (but and irreversible), prophylactic penicillin therapy is re- 24
  • 31. CHAPTER 4. STREPTOCOCCI quired for much of the patients life. This will prevent future beta-hemolytic group A streptococcal infections,which if they occur will elicit more of the cross-reactingantibodies. Once damaged, the heart valves are susceptible to in-fection by many other types of bacteria. Therefore, pa-tients with valvular disease need to be given antibioticswhenever they have a dental or surgical procedure.Amoxicillin is commonly given. The joint pain of rheumatic fever is classified as anacute migratory polyarthritis, which is to say that jointpains arise at various sites throughout the day andnight. Fortunately, there is no permanent injury to thejoints. 2) Acute post-streptococcal glomerulonephritis: This is an antibody-mediated inflammatory disease of the glomeruli of the kidney. It occurs about one week Figure 4-4 after infection of either the pharynx OR skin by nephritogenic (having the ability to cause glomeru- Neonates with meningitis do not present with a stiff neck, which is the classic sign seen in adults. Instead, lonephritis) strains of beta-hemolytic group A strepto- they display nonspecific signs, such as fever, vomiting, cocci. Fortunately, only a few strains of beta-hemolytic group A streptococci are nephritogenic. Certain anti- poor feeding, and irritability. If you even suspect menin- gitis, you must act rapidly because every minute counts.gens from these nephritogenic streptococci induce an Diagnosis of meningitis is made by a lumbar puncture.antibody response. The resulting antigen-antibody com-plexes travel to and are deposited in the glomerular Antibiotics are often started prior to the results of thebasement membrane, where they activate the comple- lumbar puncture if meningitis is suspected. The organ-ment cascade. This leads to local glomerular destruction isms that must be covered by the antibiotics include Es- cherichia coli, Listeria monocytogenes, and well as groupin the kidney. Clinically, a child will show up in your office, and his B streptococcus. These are the 3 most common patho-mother will complain that his face is puffy. This is gens associated with meningitis in infants younger thancaused by the retention of fluid from his damaged kid- 3 months of age.ney. His urine is darker than normal (tea or coca-colacolored) due to hematuria (blood in the urine). The child Viridans Group Streptococcimay also have hypervolemia secondary to fluid reten- ( No Lancefield antigen classification. Memberstion, which can cause high blood pressure. Upon further include Streptococcus salivarius, S. sanguis, S. mitis,questioning you may be able to elicit the fact that he had S. intermedius, S. mutans, and others.)a sore throat or skin infection a week or so ago. This type This is a big, heterogeneous group of streptococci thatof glomerular disease usually has a good prognosis (es- are not identified based on one Lancefield group.pecially in the pediatric population). Viridis is the Latin word for green, and most of the "Mom, my urine is tea colored!!!!" viridans streptococci are alpha-hemolytic, producing greenish discoloration on blood agar. They are normalFig. 4-4. Acute post-streptococcal glomerulonephritis human gastro-intestinal (G.I.) tract flora that are fre-causes tea colored urine (hematuria). quently found in the nasopharynx and gingival crevices. The viridans streptococci cause 3 main types of infec- tion: dental infections, endocarditis, and abscesses. GROUP B STREPTOCOCCI ( also called Streptococcus agalactiae) 1) Dental infections: Some of the viridans strepto- cocci, especially S. mutans, can bind to teeth and fer- These streptococci are also beta-hemolytic. When ment sugar, which produces acid and dental cariesthinking of group B streptococci, think of group B for (cavities!!).BABY. About 25% of women carry these bugs vaginally, and 2) Endocarditis: Dental manipulations send show-a baby can acquire these bacteria during delivery. These ers of these organisms into the bloodstream. Subse-organisms cause neonatal (< 3 months of age) meningi- quently, they can implant on the endocardial surface oftis, pneumonia, and sepsis. the heart, most commonly on a previously damaged 25
  • 32. CHAPTER 4. STREPTOCOCCIheart valve (such as from old rheumatic fever, a congen-ital heart defect, or mitral valve prolapse). These bacte-ria produce an extracellular dextran that allows them tocling to cardiac valves. This results in subacute bacter-ial endocarditis (SBE), characterized by a slow (hence"subacute") growth and piling up of bacteria on the heartvalve (like a pile of bacteria on a petri dish). Clinically,a patient with subacute bacterial endocarditis slowly de-velops low-grade fevers, fatigue, anemia, and heart mur-murs secondary to valve destruction. In contrast, acuteinfective endocarditis is caused by a staphylococcal in-fection, often secondary to IV drug abuse, and is charac-terized by an abrupt onset of shaking chills, high spikingfevers, and rapid valve destruction.Fig. 4-5. When you think of viridans streptococci,think ofVERDE, which is the word for "green" in Span-ish. Now picture the Verde (green) foliage betweensome incisors-you know, palm trees, vines, the works .When these teeth are pulled by sadistic dentists (theyall are), the Verde foliage enters the blood stream andsettles on leaflets of the heart valves, especially valveswhich have been previously damaged (such as valvesdamaged by rheumatic fever).Fig. 4-6. Viridans Streptococcus is eating heart valvesslowly, while Staphylococcus aureus is eating fast (No-tice that these organisms appear as a strip and clusterrespectively!). Viridans Streptococcus, slowly eatsaway at the valve just as a plant slowly grows into soil.This is in sharp contrast to Staphylococcus aureus, whoreceived his Olympic gold (aureus) medals for his abil-ity to rapidly bind to and destroy the heart valves.Therefore, subacute bacterial endocarditis (SBE) iscaused by viridans Streptococcus, while acute bacterialendocarditis is the disease associated with Staphylococ-cus aureus. Note that group D streptococci (discussedbelow) can also cause subacute bacterial endocarditis. Figure 4-5 Interestingly, the streptococci work together as ateam to establish SBE. Initially, Streptococcus pyo- should consider investigating with a CAT scan withgenes causes rheumatic fever, which damages the heart contrast.valves. Now, viridans Streptococcus or the group D Streptococcus InterMediUS:streptococci can more easily adhere to the heart valves IMmediately USses (asses) for ABSCESSand cause SBE!!! 3) Abscesses: There is a subgroup of the viridans GROUP D STREPTOCOCCIstreptococci called the Streptococcus intermediusgroup (comprised of Streptococcus intermedius, S. con- (Enterococci and Non-enterococci)stellatus, and S. anginosus) which are microaerophilicand are part of the normal G.I. tract flora. These oxy- Traditionally these alpha-hemolytic bacteria havegen hating critters are often found in abscesses in the been divided into two subgroups: the enterococcibrain or abdominal organs. They are found alone in (comprised of Enterococcus faecalis and Enterococcuspure cultures or in mixed cultures with anaerobes (like faecium) and the non-enterococci (comprised of many organisms including Streptococcus bovis and Strepto-Bacteroides fragilis). coccus equinus). Recently the enterococci have been A clinical pearl is that if a Streptococcus intermedius shown to be sufficiently different from the streptococcigroup bacteria grows in the blood you should suspect to be given their own genus enterococcus. S. bovis andthat there is an abscess hiding in an organ and you S. equinus are still classified as streptococci. 26
  • 33. CHAPTER 4. STREPTOCOCCI Figure 4-6 Enterococcus (faecalis and faecium) ciprofloxacin, chloramphenicol, and doxycycline. A newer class of drugs, the pristinomycins, may also be used: The enterococci take up residence in the human in- dalfopristin (Synercid) + quinupristin (RP 59500). These testines and are considered normal bowel flora. They are cause painful arthralgias in 2% and venous irritation alpha hemolytic and unique in that they all grow well in (less with a central line) in 5%. They are currently40% bile or 6.5% NaCl. Clinically, the enterococci are available for compassionate use against VRE (Rhone-commonly the infecting agents in urinary tract infec- Poulenc-Rorer, telephone 610-454-3071). To avoid furthertions, biliary tract infections (as they grow well in bile), emergence of this resistant strain and worse yet, thebacteremia, and subacute bacterial endocarditis (SBE). transfer of the genes to more virulent bugs like Staphylo-While these bugs are not as virulent as Streptococcus coccus aureus, we must limit the use of vancomycin. Forpyogenes, they are always around in the G.I. tract and example, metronidazole must be used for Clostridium dif-prey on weak hospitalized patients. In fact, the entero- Ficile pseudomembranous colitis instead of vancomycin.cocci are close to the second most common cause of noso-comial (hospitally acquired) infections in the U.S. today! Non-Enterocci (Streptococcus bovis and equinus) NEWS FLASH!!!! Read all about it! Enterococcus now resistant to ampicillin and vancomycin! Like the enterococci, Streptococcus bovis is hardy, The enterococci are resistant to most of the drugs we growing in 40% bile (but not in 6.5% NaCl). It lives in use to kill gram positive bacteria. We usually treat ente- the G.I. tract, and it causes similar diseases. rococcal infections with ampicillin plus an aminoglyco- An important unique property is that there is a re- side. However, many enterococcal strains are now markable association between S. bovis infection and resistant to both of these agents; in these cases we treat colon cancer!!! In some series 50% of people with S. bo- with vancomycin (see Fig. 16-17). Now our worst night- vis bacteremia have a colonic malignancy. We do not mare has been realized: vancomycin resistant enterococci know if S. bovis is a cause of colon cancer or just a (VRE) have developed and have been spreading in the marker of the disease. U.S. The resistance property is carried on a gene that is BOVIS in the BLOOD:transferable. Enterococci with this resistance gene alter Better Beware, CANCER in the BOWELtheir cell wall dipeptide d-alanine-d-alanine (the targetfor vancomycin, see page 141), changing it to d-alanine- Streptococcus pneumoniaelactate. This change prevents vancomycin binding. (Alias the pneumococcus; No Lancefield antigen) The treatment of multiply resistant enterococci is verydifficult and will involve complicated susceptibility test- The pneumococcus is a very important organism be-ing and infectious disease specialty consultation, and will cause it is a major cause of bacterial pneumonia andrequire us to take some old and some new antibiotics off meningitis in adults, and otitis media in children. pneu-the shelves that are sometimes active against VRE: the mococcus is to parents what group B streptococcus is toglycopeptides (like vancomycin), teicoplanin, rifampin, Babies. 27
  • 34. CHAPTER 4. STREPTOCOCCI The pneumococcus does not have Lancefield antigens! The first pneumococcal vaccine (the pneumovax) hasUnder the microscope, they appear as lancet-shaped 25 of the most common capular polysaccharide antigens.gram-positive cocci arranged in pairs (diplococci). It is given to people for whom pneumococcal pneumonia The major virulence factor of the pneumococcus is its would be exceptionally deadly, such as immunocompro-polysaccharide capsule, which protects the organism mised or elderly folk. Individuals without spleens (as-from phagocytosis. Fortunately, the capsule is anti- plenic) or with HIV disease are unable to defendgenic, and antibodies specific for the capsule can neu- themselves against encapsulated bacteria and shouldtralize the pneumococcus. The only problem is that also be vaccinated. Unfortunately, the polysaccharidethere are 84 different capsule serotypes, so surviving an vaccine has low immunogenicity and efficacy in chil-infection with this organism only provides immunity to dren. A new heptavalent conjugate vaccine contains 71 out of the 83 possible capsule types. (thus heptavalent) capsular polysaccharide antigens There are 2 important lab tests to identify the from serotypes 4, 6B, 9V, 14, 18C, 19F, and 23F conju-pneumococcus: gated with a non-toxic diphtheria-toxin protein, to in- crease its immunogenicity. This vaccine has almost 1) Quellung reaction: When pneumococci on a slide 100% efficacy in the prevention of invasive pneumococ-smear are mixed with a small amount of antiserum cal infections in children!!! Because serotypes 3, 6B, 9V,(serum with antibodies to the capsular antigens) and 14, 19F, and 23F are the most common causes of otitismethylene blue, the capsule will appear to swell. This tech- media (bold serotypes are covered by vaccine), it also hasnique allows for rapid identification of this organism. been shown to reduce cases of otitis media in children 2) Optochin sensitivity. Streptococcus pneumoniae ( Eskola, et. al. N Engl J Med 2001; 344:403-9).is alpha-hemolytic (partial hemolysis-greenish color)but Streptococcus viridans is also alpha-hemolytic! Todifferentiate the two, a disc impregnated with optochin(you dont want to know the real name) is placed on theagar dish. The growth of Streptococcus pneumoniae willbe inhibited, while Streptococcus viridans will continueto grow. Streptococcus pneumoniae is the most common causeof pneumonia in adults. Pneumococcal pneumonia oc-curs suddenly, with shaking chills (rigors), high fevers,chest pain with respirations, and shortness of breath.The alveoli of one or more lung lobes fill up with whiteblood cells (pus), bacteria, and exudate. This is seen onthe chest X-ray as a white consolidated lobe. The patientwill cough up yellow-green phlegm that on Gram stainreveals gram-positive lancet-shaped diplococci. Fig. 4-7. The "pneumococcal warrior." He is a mighty foe, with "capsule" armor, a lung emblem on his shield, and a lancet-shaped diplococcus lance. The lung em- blem on his shield shows the severe lobar pneumonia caused by this organism. Note the consolidation of the middle right lobe and the lower left lobe, which accom- pany fever and shaking chills. Streptococcus pneumoniae is also the most commoncause of otitis media (middle ear infection) in chil-dren and the most common cause of bacterial meningi-tis in adults. The classic sign of meningitis, nuchalrigidity (a stiff neck) is usually present in an adult withmeningitis.Fig. 4-8. Otitis media (in children mostly): The pneu-mococcal warriors lance zips through the ears of an en-emy soldier!! Figure 4-7Fig. 4-9. Meningitis: Our warrior is smashing his en-emys head with a hammer!!
  • 35. CHAPTER 4. STREPTOCOCCI Figure 4-8 Figure 4-9 Fig. 4-10. We see the doctor shooting a hole through Unfortunately, we are witnessing dramatic changes in our warrior (the pneumococci) with the antibody tipped the way we treat this common and dangerous critter. pneumovax (pneumococcal pneumonia vaccine). Fig. 4-11. Summary of streptococcal groups.NEWS FLASH!!!! Read all about it! Streptococcuspneumoniae now resistant to penicillins! References Certain strains of Streptococcus pneumoniae are nowshowing intermediate level resistance to penicillin (min- Davies HD, McGreer, A, et al. Invasive group A streptococcali mal inhibitory concentrations (MIC) of 0.1-1.0 micro- infections in Ontario, Canada. N. Eng. J. Med. 1996; 335:grams penicillin per ml blood) and even high level 547-54.resistance ( MIC > 2.0 micrograms/ml blood). In some Eskola J, Kilpi T, et. al. Efficacy of a pneumococcal conjugate vac-European countries 2/3 of strains have intermediate or cine against otitis media. N Engl J Med 2001; 344:403-409.high level resistance! In the U.S. about 10% of strains Holm SE, Invasive group A streptococcal infections. N. Eng. J. Med. 1996; 335: 590-591.have intermediate resistance and 1% high level resis- Mandell GL, Bennett JE, Dolin R, eds. Principles and Practice tance; the percentage is much higher in day care set- of Infectious Diseases; 4th edition. New York: Churchill Liv- tings where children are frequently given antibiotics. ingstone, 1995;1784-1865.Worse yet, the pneumococcus is also acquiring resis- Stevens DL. Invasive group A streptococcus infections. Clinicaltance to erythromycin, trimethoprim/sulfamethoxazole, Infectious Diseases 1992; 14:2-13.and chloramphenicol. Stevens DL, Gibbons AE, et al. The eagle effect revisited: effi- The good news is that high dose penicillin (1 million cacy of clindamycin, erythromycin, and penicillin in the treat-units every 4 hours) and the cephalosporins are effec- ment of streptococcal myositis. J. Infect. Dis. 1988;158:23-8.tive against bugs with intermediate level resistance. In Tuomanen EI, Austrian R, Masure HR. Mechanisms of disease:areas where high level resistant strains are common pathogenesis of pneumococcal infection. N Engl J Medvancomycin will have to be added. 1995;332(19 ):1280-1284.Figure 4-10 29
  • 36. Figure 4-11 STREPTOCOCCI M. Gladwin and B. Trattler, Clinical Microbiology Made Ridiculously Simple ©MedMaster
  • 37. CHAPTER 5. STAPHYLOCOCCI Staphylococci are forever underfoot, crawling all over cocci and mix on a slide with H2O2. If bubbles appear, hospitals and living in the nasopharynx and skin of up this indicates that H2O2 is being broken down into oxy- to 50% of people. While at times they cause no symp- gen bubbles and water; catalase-positive staphylococci toms, they can become mean and nasty. They will be one are present. of your future enemies, so know them well. 3) Culture: Staphylococcus aureus and certain streptococci are beta-hemolytic (completely hemolyze The 3 major pathogenic species are Staphylococcus red blood cells on an agar plate), but Staphylococcus au- aureus, Staphylococcus epidermidis, and Staphylococ- It is extremely important to know how to differ- reus can be differentiated from the other beta-hemolytic cus saprophyticus. entiate staphylococci from streptococci because most cocci by their elaboration of a golden pigment on sheep staphylococci are penicillin G resistant! You can do 3 blood agar. things to differentiate them-Gram stain, catalase test, and culture. Now that we can differentiate staphylococci from streptococci, it is important to know which species of staphylococcus is the actual pathogen. The key point: Of the 3 pathogenic staphylococcal species, only Staphylo- Fig. 5.1. Staphylococci lie in grape-like clusters as coccus aureus is coagulase positive!!! It elaborates the seen on Gram stain. Visualize this cluster of hospital enzyme, coagulase, which activates prothrombin, caus- staff posing for a group photo. Staphylococcus aureus is ing blood to clot. In Fig. 5-1, note how all the Gold- catalase-positive, thus explaining the cats in the group Medalists (Staphylococcus aureus) hang out together to photo. Staphylococcus aureus (aureus means "gold") show each other their gold medals. You can think of can be differentiated from the other beta-hemolytic them as coagulating together. So when a gram-positive cocci by their elaboration of a golden pigment when cul- coccus in clusters is isolated in culture, the microbiology tured on sheep blood agar. Notice that our hospital laboratory will do a coagulase test. If they report to you Staff (Staph) all proudly wear gold medals around that the test demonstrates coagulase positive grampos- their necks. itive cocci in clusters you know you have Staphylococcus aureus. If they report coagulase negative gram-positive 2) Catalase test: All staphylococci have the enzyme cocci in clusters, think of Staphylococcus epidermidis or catalase (streptococci do not!). staphylococcus saprophyticus. Fig. 5-2. Catalase testing, showing a cluster of staph- ylococci (catalase-positive) blowing oxygen bubbles. To test, rub a wire loop across a colony of gram-positiveFigure 5-1 Figure 5-2 31
  • 38. CHAPTER 5. STAPHYLOCOCCI Staphylococcus aureus This critter has a microcapsule surrounding its hugepeptidoglycan cell wall, which in turn surrounds a cellmembrane containing penicillin binding protein (alsocalled transpeptidase-see page 114). Numerous pow-erful defensive and offensive protein weapons stick outof the microcapsule or can be excreted from the cyto-plasm to wreak havoc on our bodies:Proteins That Disable OurImmune Defenses 1) Protein A: This protein has sites that bind the Fcportion of IgG. This may protect the organism from op-sonization and phagocytosis. 2) Coagulase: This enzyme can lead to fibrin forma-tion around the bacteria, protecting it from phagocytosis. Figure 5-4 3) Hemolysins (4 types): Alpha, beta, gamma, anddelta. They destroy red blood cells, neutrophils, macro- Fig. 5-4. Hapless red blood cell following a neutrophil,phages, and platelets. running to destruction at the hands of Staphylococcus 4) Leukocidins: They destroy leukocytes (white aureus and its hemolysis and leukocidin dynamite.blood cells). 5) Penicillinase: This is a secreted form of beta- Proteins to Tunnel Through Tissuelactamase. It disrupts the beta-lactam portion of the 1) Hyaluronidase ("Spreading Factor"): This pro-penicillin molecule, thereby inactivating the antibiotic tein breaks down proteoglycans in connective tissue.(see Chapter 16). 2) Staphylokinase: This protein lyses formed fibrin 6) Novel penicillin binding protein: This protein, clots (like streptokinase).also called transpeptidase, is necssary for cell wall pep- 3) Lipase: This enzyme degrades fats and oils,tidoglycan formation and is inhibited by penicillin. which often accumulate on the surface of our body. ThisSome strains of Staphylococcus aureus have new peni- degradation facilitates Staphylococcus aureus coloniza-cillin binding proteins that are resistant to penicilli- tion of sebaceous glands.nase-resistant penicillins and cephalosporins. 4) Protease: destroys tissue proteins.Fig. 5-3. Staphylococcus aureus wielding protein A Fig. 5-5. Staphylococcus aureus produces proteinsand coagulase shields, defending itself from attacking that allow the bacteria to tunnel through tissue.antibodies and phagocytosis. Exotoxin Assault Weaponry 1) Exfoliatin: A diffusible exotoxin that causes the skin to slough off (scalded skin syndrome).Figure 5- 3 Figure 5-5 32
  • 39. CHAPTER 5. STAPHYLOCOCCI Figure 5-6P 2) Enterotoxins (heat stable): Exotoxins which vomiting, diarrhea, abdominal pain, and occasionally cause food poisoning, resulting in vomiting and diarrhea. fever. The episode lasts 12 to 24 hours. 3) Toxic Shock Syndrome toxin (TSST-1): This exotoxin is analogous to the pyrogenic toxin produced by Fig. 5-7. Staphylococcus aureus gastroenteritis. "I Lancefield group A beta-hemolytic streptococci, but is told you not to eat the mayonnaise, sweetheart!" far more deadly. This exotoxin causes toxic shock 2) Toxic Shock Syndrome: You may have heard syndrome and is found in 20% of Staphylococcus about toxic shock syndrome and super-absorbent tam- aureaus isolates. These pyrogenic toxins are called superantigens and bind to the MHC class II molecules on antigen presenting cells (such as macrophages). The toxin-MHC II complex causes a massive T cell response and outpouring of cytokines, resulting in the toxic shock syndrome described below. (see Fig. 5-9). Fig. 5-6. Staphylococcus aureus produces exotoxin as- sault weaponry. Staphylococcus aureus causes a broad range of hu- man disease, and can infect almost any organ system. The diseases can be separated into 2 groups: Disease caused by exotoxin release: 1) Gastroenteritis (food poisoning). 2) Toxic shock syndrome. 3) Scalded skin syndrome. Disease resulting from direct organ invasion by the bacteria: 1) Pneumonia 2) Meningitis 3) Osteomyelitis 4) Acute bacterial endocarditis 5) Septic arthritis 6) Skin infections 7) Bacteremia/sepsis 8) Urinary tract infectionDiseases Caused by Exotoxin Release 1) Gastroenteritis: Staphylococci can grow in foodand produce an exotoxin. The victim will then eat the Figure 5-7food containing the pre-formed toxin, which then stim-ulates peristalsis of the intestine with ensuing nausea, 33
  • 40. CHAPTER 5. STAPHYLOCOCCI vomiting, and watery diarrhea (enterotoxin-like syn- drome), followed in a few days by a diffuse erythema- tous (red) rash (like scarlet fever). The palms and soles undergo desquamation (fine peeling of the skin) late in the course of the illness. The toxic shock syndrome is also associated with septic shock as described in Chapter 2: blood pressure may bottom out (frank shock) and the patient may suffer severe organ system damage (such as acute respiratory distress syndrome or acute renal failure). Treatment includes cleaning the infected foci, re- moval of the tampon or drainage of an infected wound, along with supportive care. Antibiotics can help by killing the bacteria and preventing more exotoxin from being produced. However, antibiotics are not curative because it is the exotoxin, not the bacteria, which causes the clinical manifestations.Figure 5-8 3) Staphylococcal Scalded Skin Syndrome: Thispons. It now appears that these tampons, when left in disease is similar in pathogenesis to toxic shock syn-place for a long time, in some way stimulate Staphylo- drome. A Staphylococcus aureus strain, which producescoccus aureus to release the exotoxin TSST-1. This exo- exfoliatin toxin, establishes a localized infection and re-toxin penetrates the vaginal mucosa and is a potent leases a diffusible toxin that exerts distant effects. Un-stimulator of both tumor necrosis factor (TNF) and like toxic shock syndrome, it usually affects neonatesinterleukin-1 (see page 15). TSST-1 also dramatically with local infection of the recently severed umbilicus orenhances susceptibility to endotoxin. Tampon use is not older children with skin infections. Clinically, it causesthe only cause of this syndrome, since men and non- cleavage of the middle epidermis, with fine sheets ofmenstruating woman can also be affected. skin peeling off to reveal moist red skin beneath. Heal- ing is rapid and mortality low. The doctor must rule outFig. 5-8. Infected sutures in surgical wounds, cuta- a drug allergy, since this can present similarly and mayneous and subcutaneous infections, and infections fol- result in death if the use of the offending drug is notlowing childbirth or abortion can all be foci from which halted.Staphylococcus aureus can release its TSST-1 exotoxin.Fig. 5-9. Toxic shock syndrome is caused by Staphy- Disease Resulting from Directlococcus aureus releasing TSST-1. This toxin creates Organ Invasionsymptoms that you can think of as a hybrid betweenfood poisoning (enterotoxins) and the streptococcal Fig. 5-10. Diseases caused by direct organ invasion bypyrogenic toxin that produces scarlet fever. The syn- Staphylococcus aureus. Visualize the Staph-wieldingdrome involves the sudden onset of high fever, nausea, wizard. (Note the cluster of staphylococci at the head of his staff.) The pathology includes: 1) Pneumonia: Staphylococcus aureus is a rare but severe cause of community-acquired bacterial pneumo- nia. Pneumonia is more common in hospitalized pa- tients. It usually follows a viral influenza (flu) upper respiratory illness, with abrupt onset of fever, chills, and lobar consolidation of the lung, with rapid destruc- tion of the lung parenchyma, resulting in cavitations (holes in the lung). This violent destructive pneumonia frequently causes effusions and empyema (pus in the pleural space). 2) Meningitis, Cerebritis, Brain Abscess: These patients can present with high fever, stiff neck, head- ache, obtundation, coma, and focal neurologic signs. 3) Osteomyelitis: This is a bone infection that usu- ally occurs in boys under 12 years of age. The infectionFigure 5-9 spreads to the bone hematogenously, presenting locally 34
  • 41. CHAPTER 5. STAPHYLOCOCCI Figure 5-10 with warm, swollen tissue over the bone and with sys- fection of the joint cavity. Patients complain of an temic fever and shakes. acutely painful red swollen joint with decreased range 4) Acute Endocarditis: This is a violent destruc- of motion. Staphylococcus aureus is the most common tive infection of the heart valves with the sudden onset pathogen causing this disease in the pediatric age of high fever (103-105 F°), chills, and myalgias (like a group and in adults over the age of 50. Without prompt bad flu). The patient with staphylococcal endocarditis treatment, many patients will permanently lose themay have no history of valvular disease and may not function of the involved joint. Diagnosis requires exam-have a murmur. Vegetations grow rapidly on the valve, ination of the synovial fluid, which will characteristi-causing valvular destruction and embolism of vegeta- cally appear yellowish and turbid, with a huge numbertions to the brain (left heart valve involvement) or lung of neutrophils (>100,000), as well as a positive Gram(right heart valve infected). Intravenous drug users de- stain or culture. Therapy requires drainage of the jointvelop a right-sided tricuspid valve endocarditis and may and antimicrobial therapy.present with pneumonia caused by bacterial emboliza- 6) Skin Infections: Minor skin infections are al-tion from this infected valve. Endocarditis caused by most exclusively caused by either Streptococcus pyo-Streptococcus viridans and Group D Streptococci has a genes (Group A beta-hemolytic) or by Staphylococcusmore gradual onset (see Fig. 4-6). aureus. It is clinically impossible to differentiate the two 5) Septic Arthritis: Invasion of the synovial mem- and, in fact, both may be involved. Streptococci can bebrane by Staphylococcus aureus results in a closed in- treated with penicillin G, but staphylococci are often re- 35
  • 42. CHAPTER 5. STAPHYLOCOCCIsistant. Therefore, many doctors believe all skin infec- The Centers for Disease Control reports that MRSA intions should be treated with a penicillinase-resistant hospital intensive care units has increased from approx-penicillin such as dicloxacillin. imately 20% in 1987 to 60% in 1997 and MRSA strains Skin infections caused by staphylococci or strepto- are now increasingly found in the community. Van-cocci usually follow a major or minor break in the skin, comycin must be used for the treatment of MRSA. Un-with scratching of the site spreading the infection: fortunately, strains of Staphylococcus aureus resistant to Vancomycin are now being reported. Hospital use of a) Impetigo: This contagious infection usually oc- vancomycin must be reserved for only critical indica-curs on the face, especially around the mouth. Small tions to protect this antibiotic from emerging resistance.vesicles lead to pustules, which crust over to becomehoney-colored, wet, and flaky. b) Cellulitis: This is a deeper infection of the cells. Staphylococcus epidermidisThe tissue becomes hot, red, shiny and swollen. This organism is part of our normal bacterial flora d) Local Abscesses, Furuncles, and Carbuncles: and is widely found on the body. Unlike StaphylococcusAn abscess is a collection of pus. Infection of a hair fol- aureus, it is coagulase-negative.licle produces a single pus-filled crater with a red rim. This organism normally lives peacefully on our skinThis infection can penetrate deep into the subcutaneous without causing disease. However, compromised hospi-tissue to become a furuncle. These may bore through tal patients with Foley urine catheters or intravenousto produce multiple contiguous, painful lesions commu- lines can become infected when this organism migratesnicating under the skin called carbuncles. Significant from the skin along the tubing.abscesses must be surgically drained. Staphylococcus epidermidis is a frequent skin conta- e) Wound infections: Any skin wound can be in- minant of blood cultures. Contamination occurs whenfected with Staphylococcus aureus, resulting in an ab- the needle used to draw the blood passes through skinscess, cellulitis, or both. When a sutured post-surgical covered with Staphylococcus epidermidis. Drawing bloodwound becomes infected, it must be reopened and often from 2 sites will help determine if growth of Staphylo-left open to heal by secondary intention (from the bot- coccus epidermidis represents a real bacteremic infec-tom of the wound outward). tion or is merely a contamination. If only one of the 7) Blood and catheter infections: Staphylococ- samples grows Staphylococcus epidermidis, you cancus aureus can migrate from the skin and colonize cen- suspect that this is merely a skin contaminant. How-tral venous catheters resulting in bacteremia, sepsis, ever, if 2 cultures are positive, the likelihood of bac-and septic shock (see page 12), as well as endocarditis. teremia with Staphylococcus epidermidis is high. Staphylococcus epidermidis also causes infectionsMethicillin-Resistant Staphylococcus of prosthetic devices in the body, such as prosthetic joints, prosthetic heart valves, and peritoneal dialysisaureus (MRSA) catheters. In fact, Staphylococcus epidermidis is the Most staphylococci are penicillin-resistant because most frequent organism isolated from infected in- they secrete penicillinase. Methicillin, Nafcillin, and dwelling prosthetic devices. The organisms have a poly- other penicillinase-resistant penicillins are not broken saccharide capsule that allows adherance to these down by penicillinase, thus enabling them to kill most prosthetic materials. strains of Staphylococcus aureus. MRSA is a strain ofStaphylococcus aureus that has acquired multi-drug resistance, even against methicillin and nafcillin. These Staphylococcus saprophyticusstrains tend to develop in the hospital, where broad- This organism is a leading cause (second only to E.spectrum antibiotics are used. These antibiotics apply coli)of urinary tract infections in sexually active younga selection pressure that favors multi-drug resistance in women. It is most commonly acquired by females (95%)bacteria (usually acquired by plasmid exchange-see in the community (NOT in the hospital). This organismpage 20). is coagulase-negative. MRSA is transferred from patient to patient by the Fig. 5-11. Summary chart of staphylococci.hand contact of health care workers, a strong argumentfor zealous hand-washing habits!!! This feared bacteria Recommended Review Article:is resistant to almost all antibiotics. Vancomycin isone of the few antibiotics useful in treating infectionscaused by MRSA, although organisms resistant even to Lowy FD. Medical progress: Staphylococcus aureus infections.vancomycin have been reported in the U.S. and Japan N Engl J Med 1998; 339:520-532.(MMWR 1997; 46: 813-5). 36
  • 43. Figure 5-11 M. Gladwin and B. Trattler, Clinical Microbiology Made Ridiculously Simple ©MedMaster STAPHYLOCOCCI
  • 44. CHAPTER 6. BACILLUS and CLOSTRIDIUM (SPORE-FORMING RODS)There are 6 medically important gram-positive bacte- infected animal products, such as hides or wool. In theria: 2 are cocci, and 4 are rods (bacilli). Two of the rods U.S., cases have followed contact with goat hair prod-are spore-formers and 2 are not. We have already dis- ucts from Haiti, such as drums or rugs. Human-to-cussed the 2 gram-positive cocci (streptococci and human transmission has never been reported.staphylococci). In this chapter we will examine the 2 Bacillus anthracis forms a spore which is very stable,Clostridium.gram-positive spore-forming rods, Bacillus and resistant to drying, heat, ultraviolet light, and disinfec- tants, and can survive dormant in the soil for decades. Bacillus and Clostridium cause disease by the release Once it is introduced into the lungs, intestine, or a skinof potent exotoxins (see Fig. 2-8). They differ biochemi- wound, it germinates and makes toxins. The germina-cally by their like or dislike of oxygen. Bacillus enjoys tion and expression of plasmid encoded virulence fac-oxygen (so is aerobic), while Clostridium multiply in tors (on plasmids pXOl and pX02) is regulated by anan anaerobic environment. In an air tight Closet, if increase in temperature to 37°C, carbon dioxide concen-you will! tration, and serum proteins. So the spore actually acti- vates only when introduced into the host! Because of its BACILLUS small size (1-2 µm, ideal for inhalation into alveoli), sta- bility and the nearly 100% lethality of pulmonary an- There are 2 pathogenic species of gram-positive, aer- thrax (after spore inhalation), it is considered an idealobic, spore-forming rods: Bacillus anthracis and Bacil- candidate for biological terrorism and warfare. It waslus cereus. Bacillus anthracis causes the disease used by the Japanese army in Manchuria in 1940.anthrax while Bacillus cereus causes gastroenteritis(food poisoning). Fig. 6-1. Anthony has Anthrax. This figure demon-Bacillus anthracis strates how the Bacillus anthracis spores are contracted from contaminated products made of hides and goat hair.( Anthrax) The spores can germinate on skin abrasions (cutaneous anthrax), be inspired into the lungs (respiratory anthrax), Bacillus anthracis is unique in that it is the only bac- or ingested into the gastrointestinal tract (GI anthrax).terium with a capsule composed of protein (poly-D- The spores are often phagocytosed by macrophages in theglutamic acid). This capsule prevents phagocytosis. skin, intestine, or lung and then germinate, becomingBacillus anthracis causes anthrax, a disease that pri- active (vegetative) gram-positive rods. The bacteria aremarily affects herbivores (cows and sheep). Humans are released from the macrophage, reproduce in the lym-exposed to the spores of Bacillus anthracis during direct phatic system, and then invade the bloodstream (up tocontact with infected animals or soil, or when handling 10-100 million bugs per milliliter of blood!!!). Figure 6-1 38
  • 45. CHAPTER 6. BACILLUS AND CLOSTRIDIUM (SPORE-FORMING RODS) With a cutaneous anthrax infection (the most com- vaccine composed of the protective antigen (PA). Animals mon route of entry), Bacillus anthracis rapidly multi- are vaccinated with living cultures attenuated by the loss plies and releases a potent exotoxin. This exotoxin of their antiphagocytic protein capsule. These living vac- causes localized tissue necrosis, evidenced by a painless cines are considered too dangerous for human use. round black lesion with a rim of edema. This lesion is called a "malignant pustule" because without antibiotic Bacillus cereus therapy (penicillin), Bacillus anthracis can continue to ("Be serious") proliferate and disseminate through the bloodstream, which can cause death. The skin lesion usually resolves Bacillus cereus is different from Bacillus anthracis in spontaneously in 80-90% of cases, but sometimes that it is motile, non-encapsulated, and resistant to severe skin edema and shock occur. penicillin. Bacillus cereus causes food poisoning (nau- Pulmonary anthrax, called woolsorters disease, is not sea, vomiting, and diarrhea). Food poisoning occurs actually pneumonia. The spores are taken up by when Bacillus cereus deposits its spores in food, which macrophages in the lungs and transported to the hilar and then survive the initial cooking process. The bacteria mediastinal lymph nodes where they germinate. Medi- then germinate in the food and begin releasing their en- astinal hemorrhage occurs resulting in mediastinal terotoxin. To inactivate the spores, the cooked food must widening (enlarged area around and above the heart seen be exposed to high temperatures and/or refrigeration. on chest radiograph and CT scan) and pleural effusions. Bacillus cereus can secrete 2 types of enterotoxins, Gastrointestinal anthrax frequently results in death which cause different kinds of food poisoning: and fortunately is rare. Outbreaks have followed the in- 1) A heat-labile toxin similar to the enterotoxin of gestion of spores (often from contaminated meat). Bacil- cholera and the LT from Escherichia coli (see Fig. 2-8) lus anthracis matures and replicates within the intestine, causes nausea, abdominal pain and diarrhea, lasting where it releases its exotoxin. The exotoxin causes a 12-24 hours. necrotic lesion within the intestine. Patients present with vomiting, abdominal pain, and bloody diarrhea. 2) A heat-stable toxin produces a clinical syndrome similar to that of Staphylococcus aureus food poisoning, The release of exotoxin is the major reason why an- with a short incubation period followed by severe nau- sea and vomiting, with limited diarrhea. thrax carries such a high mortality rate. These toxins are encoded on a plasmid called pXOl. The exotoxin When a patient is rushed to the hospital with food contains 3 separate proteins, which by themselves are poisoning, and examination of the food reveals B. nontoxic but together produce the systemic effects of cereus, the best way to respond when your attending or- anthrax: ders you to treat the patient with antibiotics is "Be se- rious, Dr. Goofball." Since the food poisoning is caused 1) Edema factor (EF) This is the active A subunit by the pre-formed enterotoxin of Bacillus cereus, antibi- of this exotoxin and is a calmodulin-dependent adeny- otic therapy will not alter the course of this patients late cyclase. It increases cAMP, which impairs neu- symptoms. trophil function and causes massive edema (disrupts water homeostasis). 2) Protective antigen (PA) promotes entry of EF CLOSTRIDIUM into phagocytic cells (similar to a B subunit of the other Clostridium are also gram-positive spore-formingA-B toxins, see discussion of exotoxins in Chapter 2). rods. However, they are anaerobic, and can therefore 3) Lethal factor (LF) is a zinc metalloprotease that be separated from the aerobic spore-forming rodsinactivates protein kinase. This toxin stimulates the (Bacillus) by anaerobic culture. This group of bacteria ismacrophage to release tumor necrosis factor a and in- responsible for the famous diseases botulism, tetanus,terleukin-1(3, which contribute to death in anthrax. gas gangrene, and pseudomembranous colitis. A second plasmid, pXO2, encodes three genes neces- Clostridium harm their human hosts by secreting ex-sary for the synthesis of a poly-glutamyl capsule. This tremely powerful exotoxins and enzymes. Rapid diag-capsule inhibits phagocytosis of the vegetative bacteria. nosis of a clostridial infection is crucial, or your patientBoth plasmids are critical for bacterial virulence. will die!!!! Rapid identification and prompt use of penicillin, doxy-cyclin, ciprofloxacin, or levofloxacin are critical in prevent- Clostridium botulinum ( Botulism)ing the high mortality associated with systemic infection byBacillus anthracis. Individuals taking part in high-risk ac- Clostridium botulinum produces an extremely lethaltivities (petting goats or cows in countries where this dis- neurotoxin that causes a rapidly fatal food poisoning.ease is rampant) and military personnel should be given a The neurotoxin blocks the release of acetylcholine (ACh) 39
  • 46. CHAPTER 6. BACILLUS AND CLOSTRIDIUM (SPORE-FORMING RODS)from presynaptic nerve terminals in the autonomic ner- Clostridium botulinum matures and synthesizes itsvous system and motor endplates, causing flaccid mus- neurotoxin. Those who consume the contents of the jarcle paralysis. when it is opened weeks later will be ingesting the potent neurotoxin. These afebrile patients initiallyAdult Botulism develop bilateral cranial nerve palsies causing double vision (diplopia) and difficulty swallowing (dysphagia). Eating smoked fish or home-canned vegetables is as- This is followed by general muscle weakness, whichsociated with the transmission of botulism. Clostridium rapidly leads to sudden respiratory paralysis and death.botulinum spores float in the air and can land on food. Patients must immediately be treated with an anti-If the food is cooked thoroughly, the spores will die. toxin, which can neutralize only the unbound free neu-However, if the food with the spores is not cooked suffi- rotoxin in the bloodstream. Intubation and ventilatoryciently, and is then placed into an anaerobic environ- support is critical until the respiratory muscles resumement (like a glass jar, can, or zip-lock freezer bag), activity.Figure 6-2 40
  • 47. CHAPTER 6. BACILLUS AND CLOSTRIDIUM (SPORE-FORMING RODS) Figure 6-3 Infant Botulism Infant botulism occurs when infants ingest food contaminated with Clostridium botulinum spores (cases have followed ingestion of fresh honey contami- nated with spores). The spores germinate and Clostrid- ium botulinum colonizes the infants intestinal tract. From this location, botulism toxin is released. Initially, the infant will be constipated for two to three days. This is followed by difficulty swallowing and muscle weakness. These "floppy" babies must be hospi- talized and given supportive therapy. Prognosis is ex- cellent, so antitoxin is generally not used.Fig. 6-2. Botulism. The adult is eating home-cannedbeans with neurotoxin while the infant is eating honeywith spores. The adult often requires intubation and Figure 6-4ventilatory support while the baby is merely "floppy." inhibitory neurotransmitters. This inhibition of in-Clostridium tetani hibitory interneurons allows motor neurons to send a(Tetanus) high frequency of impulses to muscle cells, which re- sults in a sustained tetanic contraction. Clostridium tetani causes tetanus, a disease that classically follows a puncture wound by a rusty nail but Fig. 6-4. Clinically, the patient with tetanus presents can follow skin trauma by any object contaminated with with severe muscle spasms, especially in the muscles of spores. Clostridium tetani spores, which are commonly the jaw (this is called trismus, or lockjaw). The af-found in soil and animal feces, are deposited in the fected patient exhibits a grotesque grinning expression,wound and can germinate as long as there is a localized called risus sardonicus, which is due to spasm of theanaerobic environment (necrotic tissue). From this lo- facial muscles. Mortality is high once the stage of lock-cation, Clostridium tetani releases its exotoxin, called jaw has been reached.tetanospasmin. The tetanus toxin ultimately causes a sustained con- Because of the high mortality of tetanus, prophylactictraction of skeletal muscles called tetany. i mmunization with formalin-inactivated toxin (tetanus toxoid) is performed once every ten years in the U. S.Fig. 6-3. Tetany occurs after the tetanus toxin is This booster serves to regenerate the circulating anti-taken up at the neuromuscular junction (end plate) and bodies against tetanus toxin, that were first generatedis transported to the central nervous system. There the via childhood immunizations. You may not remembertoxin acts on the inhibitory Renshaw cell interneurons, your first shot (you were probably just 2 months old atpreventing the release of GABA and glycine, which are the time), but all children in the U. S. are immunized 41
  • 48. CHAPTER 6. BACILLUS AND CLOSTRIDIUM (SPORE-FORMING RODS) Figure 6-5with a series of DPT (diphtheria-pertussis-tetanus) Fig. 6-5. Both botulism and tetanus can lead to res-shots at ages 2, 4, 6, and 18 months, followed by a piratory failure requiring mechanical ventilation. Inbooster before entry into school (4-6 years). This regi- botulism, there is flaccid muscle paralysis as the acetyl-men provides protection from tetanus (along with diph- choline at the motor end plate is blocked. In tetanustheria and pertussis). However, the protection from there is constant muscle contraction, as the inhibitorytetanus only lasts about 10 years so booster shots of signals are blocked. The tetanic contraction of the res-tetanus are given every 10 years. piratory muscles also results in respiratory failure. In the emergency room you will encounter 3 types ofpatients with skin wounds: Clostridium perfringens (Gas Gangrene) 1) Patients who were immunized as a child and re-ceived periodic boosters but the last shot was more Everyone has heard of gas gangrene. Prior to anti-than 10 years ago. These patients are given another biotics, Clostridium perfringens devastated soldiersbooster. wounded in battle. This bacterium, whose spores can be 2) Patients who have never been immunized. Not found in the soil, matures in anaerobic conditions andonly do these patients need a booster, but they should produce gas. The spores can contaminate wounds fromalso receive preformed antibodies to the tetanus toxin battle or other trauma. Deep wounds with lots of deadcalled human tetanus immune globulins. tissue create an anaerobic environment that offers an 3) Patients who come to the hospital having already excellent home for Clostridium perfringens. As thisdeveloped tetanus. The big picture is to clear the toxin anaerobic organism grows, it releases its battery ofand the toxin-producing bacteria and to keep the pa- exotoxin enzymes (see Fig. 2-8), causing further tissuetient alive until the toxin has cleared. This is accom- destruction.plished in the following 5 steps of therapy: Clinically, there are 2 classes of infection with Clos- a) Neutralize circulating toxin with human tridium perfringens: tetanus immune globulins. b) Give an immunization booster to stimulate the 1) Cellulitis/wound infection: Necrotic skin is patients own immune system to develop anti- exposed to Clostridium perfringens, which grows and tetanus toxin antibodies. damages local tissue. Palpation reveals a moist, spongy, c) Clean the wound, excising any devitalized tis- crackling consistency to the skin due to pockets of gas; sue, to remove any remaining source of Clostridium this is called crepitus. tetani. 2) Clostridial myonecrosis: Clostridium perfrin- d) Antibiotics (penicillin) may help to clear the gens, inoculated with trauma into muscle, secretes exo- remaining toxin-producing bacteria. toxins that destroy adjacent muscle. These anaerobic e) Provide intensive supportive therapy until the bacteria release other enzymes that ferment carbohy- toxin is cleared. Muscle relaxants may have to be drates, resulting in gas formation. A computerized to- administered, and the patient may have to be placed mogram (CT) scan reveals pockets of gas within the on a ventilator. muscles and subcutaneous tissue. As the enzymes de- 42
  • 49. CHAPTER 6. BACILLUS AND CLOSTRIDIUM (SPORE-FORMING RODS) grade the muscles, a thin, blackish fluid exudes from Clostridium difficile must be considered as a possible the skin. cause. Samples of the stool can be sent to the laboratory for a Clostridium difficile toxin test. Toxin in the stool Clostridial myonecrosis is fatal unless identified and confirms the diagnosis.treated very early. Hyperbaric oxygen, antibiotics (such Treatment includes discontinuing the initial antibi-as penicillin), and removal of necrotic tissue can be life- otic and administering metronidazole or vancomycin bysaving. mouth. Both antibiotics kill Clostridium difficile and are not absorbed orally into the bloodstream. SoClostridium difficile the METRO train and VAN cruise down the gastroin-(Pseudomembranous Enterocolitis) testinal (GI) tract, rather than being absorbed, and run over the hapless Clostridium difficile bacteria (see While you may never see a case of anthrax, tetanus, Chapter 17, Fig. 17-6).or botulism in your career, this will certainly NOTbe the case with Clostridium difficile. You will tangle Fig. 6-6. Summary of the Gram-positive spore-with this critter frequently. Clostridium difficile is the forming rodspathogen responsible for antibiotic-associated pseudo-membranous colitis (diarrhea), which can follow the useof broad spectrum antibiotics (such as ampicillin, clin- Referencesdamycin, and the cephalosporins). These antibiotics canwipe out part of the normal intestinal flora, allowing the Ciaran PK, et al. Current Concepts: Clostridium difficile Col-pathogenic Clostridium difficile that is sometimes pre- itis. NEJM 1994;330:257-262.sent to superinfect the colon. Once Clostridium difficile Recommended Review Article:grows in abundance, it then releases its exotoxins.Toxin A causes diarrhea, and Toxin B is cytotoxic to the Dixon TC, Meselson M, et al. Medical Progress: Anthrax. Ncolonic cells. This disease is characterized by severe di-arrhea, abdominal cramping, and fever. Engl J Med 1999;341:815-826. Hogenauer C, et al. Mechanisms and Management of Antibiotic-Because of Clostridium difficile it becomes very Associated Diarrhea. Clinical Infectious Disease 1998;27:difficile (difficult) to give patients antibiotics. Pellizzari R, et al. Tetanus and Botulism Neurotoxins: mecha- 702-710. Examination by colonoscopy can reveal red inflamed nisms of action and therapeutic uses. Philosophical Trans- actions of the Royal Society of London 1999;354:259-268.mucosa and areas of white exudate called pseudo- Petit L. Clostridium perfringens: toxinotype and genotype.membranes on the surface of the large intestine.Necrosis of the mucosal surface occurs underneath the Shapiro R. Botulism in the United States: A Clinical and Epi- Trends in Microbiology March 1999;7:104.pseudomembranes. When a patient develops diarrhea while on antibi- demiologic Review. Ann Intern Med 1998;129:221-228.otics (or within a month of being on antibiotics), 43
  • 50. M. Gladwin and 8. Trattler, Clinical Microbiology Made Ridiculously Simple aviedMasterFigure 6-6 GRAM-POSITIVE SPORE-FORMING RODS
  • 51. CHAPTER 7. CORYNEBACTERIUM AND LISTERIA (NON-SPORE-FORMING RODS) We have examined the only 2 gram-positive cocci (Strep- target tissue, so this must be administered quickly to tococcus and Staphylococcus) and the 2 gram-positive prevent damage to the heart and nervous system. spore-producing rods ( Bacillus and Clostridium). Now 2) Penicillin or erythromycin: Either antibiotic we will discuss the other 2 gram-positive rods (both non- will kill the bacteria, preventing further exotoxin re- spore-formers): Corynebacterium diphtheriae and Liste- lease and rendering the patient non-contagious. ria monocytogenes. Both of these gram-positive rods 3) DPT vaccine: The child must receive the DPT infect patients in the pediatric age group. vaccine, as infection by Corynebacterium diphtheriae CORYNEBACTERIUM DIPHTHERIAE does not always result in immunity to future infection by this organism. The DPT vaccine stands for: D = Diphtheria; P = Pertussis (Whooping Cough); and Corynebacterium diphtheriae is the pathogen respon- T = Tetanus. The diphtheria portion contains formalin sible for diphtheria. It colonizes the pharynx, forming a i nactivated diphtheria toxin (see Chapter 6, page 41, for grayish pseudomembrane composed of fibrin, leuko- more on DPT). cytes, necrotic epithelial cells, and Corynebacterium diphtheriae cells. From this site, the bacteria release a Now that therapy has been administered, we can sit powerful exotoxin into the bloodstream, which specifi- back, relax, and confirm our clinical suspicion of diph- cally damages heart and neural cells by interfering with theria. On the potassium-tellurite plate, colonies of protein synthesis. Corynebacterium diphtheriae become gray to black within 24 hours. With Loefflers coagulated blood Fig. 7-1. Visualize the invading Corynebacterium serum, incubation for 12 hours followed by staining diphtheriaeorganisms as a tiny invading army overrun- with methylene blue will reveal rod-shaped pleomor- ning the throat and building a launching platform on phic bacteria. the pharynx. The army quickly constructs exotoxin rock- Fortunately for nonimmunized children, not all ets. From the safety of their pharynx base, they fire off Corynebacterium diphtheriae secrete this exotoxin. Just deadly rockets to the heart and central nervous system. as Group A beta-hemolytic streptococci must first be l ysogenized by a temperate bacteriophage to produce While working in the pediatric emergency room, you the erythrogenic toxin that causes scarlet fever,see a child with a sore throat and fever. There is a dark Corynebacterium diphtheriae first must be lysogenizedinflammatory exudate on the childs pharynx, which ap- by a temperate bacteriophage which codes for the diph-pears darker and thicker than that of strep throat. Al- theria exotoxin.though you may feel the urge to scrape off this tightly This powerful exotoxin contains two subunits. The Badherent pseudomembrane, you must resist this temp- subunit binds to target cells and allows the A subunit totation, because bleeding will occur and the systemic ab- enter the cell. Once inside the cell, the A subunit blockssorption of the lethal exotoxin will be enhanced. protein synthesis by inactivating elongation factor Being the brightest medical student in the pediatric ( EF2), which is involved in translation of eucaryotic mRNA into proteins (See Fig. 2-S). Notice an interest-emergency room, you immediately recognize that this ing comparison: Anti-ribosomal antibiotics are specifi-child probably has diphtheria. Realizing that you are cally designed to inhibit protein synthesis in bacterialdealing with an extremely powerful exotoxin, you ( procaryotic) cells. Similarly, this exotoxin specificallyquickly TELL yoUR InTErn not to "loaf around" (Lo- inhibits protein synthesis in humans (eucaryotes). Thusefflers). Immediately send the throat and nasopharynx this exotoxin can be considered a "human antibiotic,"swabs for culture on potassium tellurite agar and because its damage to heart and neural cells can beLoefflers coagulated blood serum media. However, lethal.these culture results will not be ready for days!!! You LISTERIA MONOCYTOGENESmay try a Gram stain of a specimen from the pseudo-membrane, but gram-positive rods are not always seen.Since there is no time to loaf with diphtheria, it is oftenbest to proceed rapidly to treatment via the following 3- If your attending or professor ever blurts out the sillystep method. statement, "Gram-negative organisms have endotoxin while gram-positive organisms do not," you can proudly 1) Antitoxin: The diphtheria antitoxin only inacti- point out that Listeria monocytogenes, a gram-vates circulating toxin, which has not yet reached its positive motile rod, actually has endotoxin! Al- 45
  • 52. CHAPTER 7. CORYNEBACTERIUM AND LISTERIA (NON-SPORE FORMING RODS) though the clinical relevance of this fact is debatable, it is wonderful for that rare moment when you actually impress your attending. If your attending, in retaliation, then attempts to pimp you into submission, describe how Listeria mono. cytogenes exhibits a tropism for nervous tissue, and thus is a common cause of meningitis in 2 particular groups. The first group is neonates, who contract this organism from their asymptomatic mothers during delivery. Lis- teria monocytogenes is the third most common cause of neonatal meningitis, following only group B streptococci and Escherichia coli. The second group of patients at risk for Listeria meningitis is immunosuppressed pa- tients, such as those with cancer, renal transplants, or AIDS. The mortality rate for meningitis in this second group is extremely high. You may wonder why this organism invades neonates and certain immunosuppressed patients but not an immune competent host. The main reason is that Lis- teria monocytogenes is a resistant fellow, able to hide out and survive within certain immune cells, such as macrophages and neutrophils that can phagocytose, or engulf, foreign objects such as bacteria. Since they can survive either outside or within cells, Listeria mono- cytogenes is called a facultative intracellular organ- ism (see Fig. 2-7). However, in immune competent hosts, the immune system can release factors that acti- vate the macrophage, so that these cells can now destroy the "vagrant" bacteria within them. Immunologists re- fer to this immune system-mediated method of destroy- ing Listeria as cell-mediated immunity. However, neonates (up to 3 months of age) and immuno sup- pressed patients are unable to activate their phagocytic cells, thus allowing Listeria monocytogenes to flourish and infect the meninges. Since pregnancy may also de- press cell-mediated immunity, Listeria monocytogenes can infect pregnant women as well, who may develop meningitis or remain asymptomatic carriers. Fig. 7-2. A) The macrophage of a neonate or an im- munosuppressed patient. B) The macrophage of an im- mune competent person. When meningitis develops in a patient who is at high risk for Listeria monocytogenes, it is important to treat it empirically with antibiotics that will cover this bac- terium. After a lumbar puncture confirms that this is a bacterial meningitis (cerebrospinal fluid analysis reveals a high number of neutrophils, a high protein level, a low glucose, and the Gram stain of the cerebrospinal fluid may demonstrate gram-positive rods), we must add ei- ther ampicillin or trimethoprim-sulfamethoxazole to the antibiotic regimen. These are 2 antibiotics that cover Listeria monocytogenes.Figure 7-1 Fig. 7-3. Summary of the non-spore-forming gram- positive rods. 46
  • 54. gore 7-i NON SPORE-FORMING GRAM-POSITIVE RODS M Gladwin and B Trattler. Clinical Microbiology Made Ridiculously Simple ©MedMastei
  • 55. GRAM-NEGATIVE BACTERIA CHAPTER 8. NEISSERIA NEISSERIA SEEN UNDER THE MICROSCOPE I I 1 NEISSERIA MENINGITIDIS NEISSERIA GONORRHOEAE Figure 8-1Its time to examine the only pathogenic gram-negative Fig. 8-1. Meet the 2 pathogenic kidney beans, whichcocci, Neisseria. These guys hang out in pairs and are have been removed from the microscope slide. They arethus called diplococci. Each coccus is shaped like a kid- sitting together at the breakfast table. Notice that theyney bean, and a pair of cocci sticks together with their sit facing each other, forming a gram-negative doughnut-concave sides facing each other, almost making the shaped diplococcus. The bean on the left, Neisseriadiplococcus look like a small doughnut. meningitidis, drinks a pot of coffee and becomes very Two species cause disease in humans: Neisseria nervous and irritable (central nervous system ir-meningitidis and Neisseria gonorrhoeae. ritation-meningitis). The other pathogenic kidney 49
  • 56. CHAPTER 8. NEISSERIAbean is Neisseria gonorrhoeae, who is a pervert (notice United States are placed together in close quarters andhow he is displaying the latest center-fold pin-up). He must survive "boot camp." In this close-knit group, car-enjoys hanging out on sexual organs and swimming in rier rates are greater than 40%. Each army recruit may"sexual fluids." He causes the sexually transmitted be a carrier of a particular strain of meningococcus thatdisease (STD) gonorrhea. the other army recruits immune systems have never been exposed to, increasing susceptibility to invasive NEISSERIA MENINGITIDIS disease. Further, due to the mentally and physically ex- hausting training, the immune systems ability to de- Besides causing meningitis, Neisseria meningi- fend itself is weakened.tidis (also called the meningococcus) causes life-threatening sepsis (meningococcemia). Virulence factors of the meningococcus include: Meningococcal Disease 1) Capsule: A polysaccharide capsule surrounds the Neisseria meningitidis spreads via respiratory se-bacterium and is antiphagocytic, as long as there are no cretions and usually lives asymptomatically in thespecific antibodies to coat (opsonize) the bacterium. nasopharynx. Rarely, the bacteria will invade the blood-Neisseria meningitidis is classified into serogroups stream (bacteremia) from the nasopharynx, resulting inbased on different capsular polysaccharides, which are meningitis and/or deadly sepsis (called meningococ-antigenic (stimulate a human antibody response). cemia). The classic "clue" to an invasive meningococcalThere are 9 serotypes of meningococcus (designated A, infection is the appearance of a petechial rash. ThisB, C, D, X, Y, Z, W135, and 29E). Meningitis is caused rash is due to the release of endotoxin from theby groups A, B, and C. meningococcus, causing vascular necrosis, an inflam- 2) Endotoxin (LPS): The meningococci can release matory reaction, and hemorrhage into the surroundingblebs of endotoxin, which causes blood vessel destruc- skin. Note that the diplococci can be seen (Gram stain)tion (hemorrhage) and sepsis (Chapter 2, page 12). The or cultured from biopsies of the petechiae.blood vessel hemorrhage is seen on the skin as tiny,round, red dots of hemorrhage called petechiae (a pe-techial rash). This same hemorrhaging process can 1) Meningococcemia: The intravascular multipli-damage the adrenal glands. cation of Neisseria meningitidis results in an abrupt on- 3) IgA1 protease: This is only found in pathogenic set of spiking fevers, chills, arthralgia (joint pains), andspecies of Neisseria. This enzyme cleaves IgA (a type of muscle pains, as well as the petechial rash. These pa-antibody) in half. tients usually look acutely ill. Once in the bloodstream, 4) Neisseria meningitidis can extract iron from hu- the meningococci rapidly disseminate throughout theman transferrin via a non-energy requiring mechanism. body. This can lead to meningitis and/or fulminant meningococcemia. Although Neisseria meningitidis has all of the above 2) Fulminant meningococcemia (Waterhouse-virulence factors, it usually blends in and becomes part Friderichsen syndrome): This is septic shock (seeof the normal flora of the nasopharynx. These individu- Chapter 2, page 12). Bilateral hemorrhage into theals (about 5% of the population) are called carriers. Car- adrenal glands occurs, which causes adrenal insuffi-riers are lucky, as this asymptomatic nasopharyngeal ciency. Abrupt onset of hypotension and tachycardia oc-infection allows them to develop anti-meningococcal an- curs, along with rapidly enlarging petechial skintibodies (this is called natural immunization). lesions. Disseminated intravascular coagulation (DIC) High-risk groups are: and coma may develop. Death can occur rapidly (6-8 1) Infants aged 6 months to 2 years hours). 2) Army recruits 3) Meningitis: This is the most common form of meningococcal disease, usually striking infants < 1 During pregnancy, maternal protective antibodies year of age. Infants usually display nonspecific findingscross the placenta and provide protection to the new- of an infection, including fever, vomiting, irritability,born, but only for the first few months of life. Infants and/or lethargy. A bulging open anterior fontanelle maywill not manufacture their own protective antibodies for be a sign of meningitis in neonates, while slightly oldera few years. Therefore, there is a window period (from infants may display a stiff neck, as well as positiveage 6 months to 2 years) when infants are extremely Kernigs and Brudzinskis signs.susceptible to a meningococcal infection (meningitis or The classic petechial skin rash may occur whensepticemia). Note that Haemophilus influenzae has a meningococcemia occurs in conjunction with meningi-similar antibody-free window. tis. This allows the physician to make a presumptive A second scenario for an invasive meningococcal in- diagnosis of meningococcal meningitis even before per-fection occurs when army recruits from all over the forming a diagnostic spinal tap. 50
  • 57. CHAPTER 8. NEISSERIA Diagnosis involves Gram stain and culture of the 2) Protein II: This outer membrane protein is also meningococcus from blood, cerebrospinal fluid, or pe- involved in adherence to host cells. techial scrapings. Neisseria grow best on blood agar that has been heated so that the agar turns brown (called Gonococcal Disease in Men chocolate agar). The classic medium for culturing Neis- A man who has unprotected sex with an infected seria is called the Thayer-Martin VCN media. This is chocolate agar with antibiotics, which are included to person can acquire a Neisseria gonorrhoeae infection. kill competing bacteria. This organism penetrates the mucous membranes of the urethra, causing inflammation of the urethra (urethri- V stands for vancomycin, which kills gram-positive tis). Although some men will remain asymptomatic, organisms. most will complain of painful urination along with a pu- rulent urethral discharge (pus can be expressed from the tip of the penis). Both asymptomatic and sympto- C stands for colistin (polymyxin) which kills all matic men can pass this infection to another sexual gram-negative organisms (except Neisseria). partner. Possible complications of this infection include epi- N stands for nystatin, which eliminates fungi. didymitis, prostatitis, and urethral strictures. Fortu- nately, this disease is easily cured by a small dose of Therefore, only Neisseria (both Neisseria meningi- ceftriaxone. tidis and Neisseria gonorrhoeae) are able to grow on this culture medium. The addition of a high concentration of Gonococcal Disease in Women CO2 further promotes the growth of Neisseria. In the laboratory, the differentiation between the Like men, women can also develop a gonococcal ure- Neisseria species is based on Neisseria meningitidis thritis, with painful burning on urination and purulent ability to produce acid from maltose metabolism, while discharge from the urethra. However, urethritis in Neisseria gonorrhoeae cannot! women is more likely to be asymptomatic with minimal Prompt treatment with penicillin G or ceftriaxone urethral discharge. is required at the first indication of disseminated Neisseria gonorrhoeae also infects the columnar ep- meningococcemia. Close contacts of an infected patient ithelium of the cervix, which becomes reddened and fri- are treated with rifampin. Immunization with purified able, with a purulent exudate. A large percentage of capsular polysaccharides from certain strains (groups women are asymptomatic. If symptoms do develop, the A, C, Y, and W135) is currently available and used for woman may complain of lower abdominal discomfort, epidemics and in high-risk groups. The group B poly- pain with sexual intercourse (dyspareunia), and a puru- saccharide does not induce immunity, so a vaccine is not lent vaginal discharge. Both asymptomatic and sympto- available at present. matic women can transmit this infection. A gonococcal infection of the cervix can progress to pelvic inflammatory disease (PID, or "pus in dere"). NEISSERIA GONORRHOEAE PID is an infection of the uterus (endometritis), fal- lopian tubes ( salpingitis), and/or ovaries ( oophori- Neisseria gonorrhoeae, often called the gonococcus, tis). Clinically, patients can present with fever, lowercauses the second most commonly transmitted sexual abdominal pain, abnormal menstrual bleeding, anddisease, gonorrhea (chlamydial infections are slightly cervical motion tenderness (pain when the cervix ismore common). moved by the doctors examining finger). Menstrua- Virulence factors of the gonococcus include: tion allows the bacteria to spread from the cervix to the upper genital tract. It is therefore not surprising 1) Pili: Neisseria gonorrhoeae has complex genes that over 50% of cases of PID occur within one week coding for their pili. These genes undergo multiple re- of the onset of menstruation. The presence of an in- combinations, resulting in the production of pili with trauterine device (IUD) increases the risk of a cervical hypervariable amino acid sequences. These changing gonococcal infection progressing to PID. Chlamydia antigens in the pili protect the bacteria from our anti- trachomatis is the other major cause of PID (see Chap-bodies, as well as from vaccines aimed at producing an- ter 12, pages 80-82).tibodies directed against the pili. The pili adhere to host cells, allowing the gonococ- Complications of PID include:cus to cause disease. They also serve to prevent phago-cytosis, probably by holding the bacteria so close to 1) Sterility: The risk of sterility appears to increasehost cells that macrophages or neutrophils are unable with each gonorrhea infection. Sterility is most com-to attack. monly caused by scarring of the fallopian tubes, which 51
  • 58. CHAPTER 8. NEISSERIAoccludes the lumen and prevents sperm from reaching Chlamydia eye infections are also a threa,ythro-the ovulated egg. erythromycin eye drops, which are effective against both 2) Ectopic pregnancy: The risk of a fetus devel- Nisseria gonorrhoeae and Chlamydia, are given to alloping at a site other than the uterus is significantly newborns. Gonococcal conjunctivitis can also occur inincreased with previous fallopian tube inflammation adults.(salpingitis). The fallopian tubes are the most commonsite for an ectopic pregnancy. Again, with scarring down Diagnosis and Treatmentof the fallopian tubes, there is resistance to normal eggtransit down the tubes. Diagnosis of Neisseria gonorrhoeae infection is best 3) Abscesses may develop in the fallopian tubes, made by Gram stain and culture on Thayer-Martinovaries, or peritoneum. VCN medium. Pus can be removed from the urethra by 4) Peritonitis: Bacteria may spread from ovaries inserting a thin sterile swab. When this is Gram stainedand fallopian tubes to infect the peritoneal fluid . and examined under the microscope, the tiny doughnut- 5) Peri-hepatitis (Fitz-Hugh-Curtis syndrome): shaped diplococci can be seen within the white bloodThis is an infection by Neisseria gonorrhoeae of the cap- cells.sule that surrounds the liver. A patient will complain of In the past, the combination of penicillin G withright upper quadrant pain and tenderness. This syn- probenicid was the regimen of choice. However, theredrome may also follow chlamydial pelvic inflammatory arose penicillinase-producing gonococcal strains anddisease. now an even tougher strain, with chromosomally- mediated antibiotic resistance to many antibiotics,Gonococcal Disease in Both Men such as tetracycline, erythromycin, and trimethoprim)and Women sulfamethoxazole. This resistance is mediated by a block in antibiotic penetration into the bacterial cell. 1) Gonococcal bacteremia: Rarely, Neisseria gon- The current therapy of choice is ceftriaxone, a thirdorrhoeae can invade the bloodstream. Manifestations generation cephalosporin (see page 131). Ceftriaxoneinclude fever, joint pains, and skin lesions (which usu- will also treat syphilis. If the patient is allergic toally erupt on the extremities). Pericarditis, endocardi- cephalosporins, spectinomycin or ciprofloxacin can betis, and meningitis are rare but serious complications of used as an alternative. The patient should also be treateda disseminated infection. at the same time with doxycycline or azithromycin for 2) Septic arthritis: Acute onset of fever occurs Chlamydia trachomatis, because up to 50% of patientsalong with pain and swelling of 1 or 2 joints. Without will be concurrently infected with this beta-lactam-re-prompt antibiotic therapy, progressive destruction of sistant (ceftriaxone included) bacteria.the joint will occur. Examination of synovial fluid usu-ally reveals increased white blood cells. Gram stain and BRANHAMELLA CATARRHALISculture of the synovial fluid confirms the diagnosis, re- (formerly called Neisseria catarrhalis)vealing gram-negative diplococci within the white bloodcells. Gonococcal arthritis is the most common kind ofseptic arthritis in young, sexually active individuals. This organism is part of the normal respiratory flora but can cause otitis media, sinusitis, bronchitis, andGonococcal Disease in Infants pneumonia (all respiratory tract illnesses). Pneumonia Neisseria gonorrhoeae can be transmitted from a usually occurs in patients with lung disease. These bac-pregnant woman to her child during delivery, resulting teria produce beta-lactamase and are thus resistant toin ophthalmia neonatorum. This eye infection usu- penicillin. Fig. 8-2. Summary of occurs on the first or second day of life and can dam-age the cornea, causing blindness. Because neonatal 52
  • 59. M. Gladwin and B. Trattler, Clinical Microbiology Made Ridiculously Simple ©MedMasterFigure 8-2 NEISSERIA
  • 60. CHAPTER 9. THE ENTERICSThe enterics are gram-negative bacteria that are part of tart properties of Escherichia coli. Follow this discus-the normal intestinal flora or cause gastrointestinal dis- sion for the overall big picture.ease. The family, genus, and species of all the enterics are You are traveling through Uruguay and wind up in aorganized in the chart at the end of this chapter so that village whose people are suffering from a terrible diar-you will not be confused with the different names. Many rhea. After giving intravenous fluids to scores of babies,of these bacteria are referred to simply by their genus you start to wonder whether the cause of this infectionname because there are so many different species in some can be eradicated. When questioned, the villagers tellgroups. The main groups are Enterobacteriaceae, Vib- you that they obtain their water from a common river.rionaceae, Pseudomonadaceae and Bateroidaceae. You know that the enterics are transmitted by the fecal- These organisms are also divided into groups based oral route, and you begin to wonder if there is fecal con-upon biochemical and antigenic properties. tamination of the river water. How will you prove that the water is fecally contaminated? Escherichia coli to the rescue! You see, EscherichiaBiochemical Classification coli is a coliform, which means that it is a normal in- Some of the important biochemical properties of the habitant of the intestinal tract. Think of E. coli = coli-organisms, which can be measured in the lab, are: form = colon. Escherichia coli is normally not found outside the intestine. So if you find Escherichia coli in 1) The ability to ferment lactose and convert it the village stream water, it does not necessarily meaninto gas and acid (which can be visualized by including that Escherichia coli is causing the diarrhea, but it doesa dye that changes color with changes in pH). Escher tell you that there is fecal matter in the river and thatichia coli and most of the enterobacteriaceae ferment some enteric may be responsible. You pull out your tat-lactose while Salmonella, Shigella and Pseudomonas tered copy of Clinical Micro Made Ridiculously Simpleaeruginosa do not. and begin the test. 2) The production of H2S, ability to hydrolyze urea, 1) Presumptive Test: You add the river water sam-liquefy gelatin, and decarboxylate specific amino acids. ples to test tubes containing nutrient broth (like agar) Some growth media do 2 things at once: 1) They con- that contains lactose. These tubes contain an invertedtain chemicals that inhibit the growth of gram-positive vial that can trap gas and a dye indicator that changesbacteria that may be contaminating the sample. 2) They color if acid is produced. You let the sample grow for ahave indicators that change color in the presence of lac- day. If lactose is fermented, gas is produced and the dyetose fermentation. The 2 that you should know are: is visualized. You now know that either Escherichia coli or a nonenteric bacteria that ferments lactose is in the 1) EMB agar (Eosine Methylene Blue): Methylene water. To find out which you inhibits gram-positive bacteria, and colonies of lac- 2) Confirmed Test: Streak EMB agar plates withtose fermenters become deep purple to black in this the water samples, and the Escherichia coli should formmedium. Escherichia coli colonies take on a metallic colonies with a metallic green sheen. Also Escherichiagreen sheen in this medium. coli can grow at 45.5C° but most nonenterics cannot, so 2) MacConkey agar: Bile salts in the medium in- you can grow 2 plates at 45.5C° and 37C° and comparehibit gram-positive bacteria, and lactose fermenters de- the colonies on both.velop a pink-purple coloration. 3) Completed Test: Colonies that were metallic green are placed in the broth again. If they produce acid In todays modern laboratories there are plastic trays and gas, then you know the river water contains Es-with up to 30 different media that measure many bio- cherichia coli.chemical reactions, including those just described. A You travel upstream and find an outhouse that hascolony of unknown bacteria is inoculated onto each been built in a tree hanging over the water. You informmedium and incubated. A computer then interprets the the villagers about the need to defecate in areas that doresults and identifies the bacteria. not have river runoff and teach them to build latrines. Within a few weeks the epidemic has ended!Fecal Contamination of Water Antigenic Classification A classic method for determining whether water hasbeen contaminated with feces demonstrates some of the The enterics form many groups, based on cell surfacepractical uses of biochemical reactions and some impor- structures that bind specific antibodies (antigenic de- 54
  • 61. CHAPTER 9. THE ENTERICS Pathogenesis The organisms in this chapter produce 2 types of dis- ease: 1) Diarrhea with or without systemic invasion. 2) Various other infections including urinary tract infections, pneumonia, bacteremia, and sepsis, es- pecially in debilitated hospitalized patients. Diarrhea A useful concept in understanding diarrhea produced by these organisms is that there are different clinical manifestations depending on the "depth" of intestinal invasion: 1) No cell invasion: The bacteria bind to the in- testinal epithelial cells but do not enter the cell. Diar- rhea is caused by the release of exotoxins (called enterotoxins in the GI tract), which causes electrolyte and fluid loss from intestinal epithelial cells or epithelial cell death. Watery diarrhea without systemic symp- toms (such as fever) is the usual picture. Enterotoxi- genic Escherichia coli and Vibrio cholera are examples. 2) Invasion of the intestinal epithelial cells: The bacteria have virulence factors that allow binding and invasion into cells. Toxins are then released that de- stroy the cells. The cell penetration results in a systemic i mmune response with local white blood cell infiltration (leukocytes in the stool) as well as fever. The cell death ples: Enteroinvasive Escherichia coli, Shigella, and Sal- results in red blood cell leakage into the stool. Exam- monella enteritidis. 3) Invasion of the lymph nodes and blood- stream: Along with abdominal pain and diarrhea con-Figure 9-1 taining white and red cells, this deeper invasion results in systemic symptoms of fever, headache, and whiteterminants). The enterics have 3 major surface anti- blood cell count elevation. The deeper invasion can alsogens, which differ slightly from bug to bug. result in mesenteric lymph node enlargement, bactere- mia, and sepsis. Examples: Salmonella typhi, Yersinia 1) 0 antigen: This is the most external component enterocolitica, and Campylobacter jejuni.of the lipopolysaccharide (LPS) of gram-negative bacte-ria. The 0 antigen differs from organism to organism,depending on different sugars and different side-chainsubstitutions. Remember O for Outer (see Fig. 1-6, for Various Other Infections The enterics are normal intestinal inhabitants andmore information on LPS). usually live with us in peaceful harmony. In the hospi- 2) K antigen: This is a capsule (Kapsule) that covers tal and nursing homes, however, some bad things hap-the 0 antigen. pen. They acquire antibiotic resistance and can cause 3) H antigen: This antigenic determinant makes up disease in debilitated patients. They can invade the de-the subunits of the bacterial flagella, so only bacteria bilitated patients when Foley catheters are in the ure-that are motile will possess this antigen. Shigella does thra or when a patient aspirates vomitus that has beennot have an H antigen. Salmonella has H antigens that colonized by the enterics. Because of this hospital ac-change periodically, protecting it from our antibodies. quisition, you will often hear them described as the hospital-acquired gram-negatives or nosocomialFig. 9-1. The 0 antigen forms the outer part of the cell gram-negatives. Examples: Escherichia coli, Kleb-membrane, the K antigen wraps around the cell like a cap-sule, and the arms of the H antigen become wavy flagella. 55
  • 62. CHAPTER 9. THE ENTERICSsiella pneumoniae, Proteus mirabilis, Enterobacter, Ser- named after the Aztec chief killed at the hands of theratia, and Pseudomonas aeruginosa. Spanish explorer, Cortez. The severity of Escherichia coli diarrhea depends on which virulence factors the strain of Escherichia FAMILY ENTEROBACTERIACEAE coli possesses. We will discuss 3 groups of diarrhea- producing Escherichia coli. These have been namedEscherichia coli based on their virulence factors and the different diar- Escherichia coli normally resides in the colon without rheal diseases they cause.causing disease. However, there is an amazing amountof DNA being swapped about among the enterics by con- 1) Enterotoxig enic Escherichia coli (ETEC):jugation with plasmid exchange, lysogenic conversion This Escherichia coli causes travelers diarrhea. It hasby temperate bacteriophages, and direct transposon pili (colonization factor) that help it bind to intestinalmediated DNA insertion (see Chapter 3). When Es- epithelial cells, where it releases exotoxins that are sim-cherichia coli acquires virulence in this manner, it can ilar to the cholera exotoxins discussed on page 62. Thecause disease: toxins are the heat labile toxin (LT), which is just like the cholera toxin, and the heat stabile toxin (ST). Nonpathogenic Escherichia coli (normal These exotoxins inhibit the reabsorption of Na and CL flora) + Virulence factors = DISEASE. and stimulate the secretion of Cl - and HCO3 - into the intestinal lumen. Water follows the osmotic pull of these Virulence factors include the following: ions, resulting in water and electrolyte loss. This pro- duces a severe watery diarrhea with up to 20 liters be- 1) Mucosal interaction: ing lost a day!!! The stool looks like rice water just a) Mucosal adherence with pili (colonization like cholera! factor). 2) Enterohemorrhagic Escherichia coli (EHEC): b) Ability to invade intestinal epithelial cells. These Escherichia coli also have a pili colonization 2) Exotoxin production: factor like the ETEC but differ in that they secrete a) Heat-labile and stable toxin (LT and ST). the powerful Shiga-like toxin ( also called verotoxin) b) Shiga-like toxin. that has the same mechanism of action as the Shigella 3) Endotoxin: Lipid A portion of lipopolysaccharide toxin (see page 58). They both inhibit protein synthesis( LPS). by inhibiting the 60S ribosome, which results in 4) Iron-binding siderophore: obtains iron from hu- intestinal epithelial cell death. So these bacteria holdman transferrin or lactoferrin. onto the intestinal epithelial cells and shoot away with the Shiga-like toxin (see Fig. 9-3). The diarrhea is Diseases caused by Escherichia coli in the presence bloody (hemorrhagic), accompanied by severe abdomi-of virulence factors include the following: nal cramps, and is called hemorrhagic colitis. Hemolytic uremic syndrome (HUS) with anemia, 1) Diarrhea. thrombocytopenia (decrease in platelets), and renal fail- 2) Urinary tract infection. ure (thus uremia), is associated with infection by a 3) Neonatal meningitis. strain of EHEC, called Escherichia coli 0157:H7. Nu- 4) Gram-negative sepsis, occurring commonly in de- merous outbreaks have occurred secondary to infectedbilitated hospitalized patients. hamburger meat served at fast food chains, suggesting that cattle may be a reservoir for EHEC.Escherichia coli Diarrhea 3) Enteroinvasive Escherichia coli ( EIEC): This disease is the same as that caused by Shigella (page 58). Escherichia coli diarrhea may affect infants or adults. In fact, the main virulence factor is encoded in a plas-Infants worldwide are especially susceptible to Es- mid shared by Shigella and Escherichia coli. This plas-cherichia coli diarrhea, since they usually have not yet mid gives the bacteria the ability to actually invade thedeveloped immunity. Since water lost in the stool is of- epithelial cells. EIEC also produces small amounts often not adequately replaced, death from Escherichia Shiga-like toxin. The host tries to get rid of the invadingcoli diarrhea is usually due to dehydration. About 5 mil- bacteria, and this results in an immune-mediated in-lion children die yearly from this infection. flammatory reaction with fever. White blood cells in- Adults (and children) from developed countries, trav- vade the intestinal wall, and the diarrhea is bloody witheling to underdeveloped countries, are also susceptible white blood cells. Like shigellosis!to Escherichia coli diarrhea, since they have not devel-oped immunity during their childhood. This travelers Fig. 9-2. Vibrio cholera, Escherichia coli, and Shigelladiarrhea is the so-called Montezumas revenge dysenteriae all holding hands. Escherichia coli can 56
  • 63. CHAPTER 9. THE ENTERICS hospitalized patients. Septic shock (see Chapter 2, page 12) due to the lipid A component of the LPS is usually the cause of death. Escherichia coli Pneumonia Escherichia coli is a common cause of hospital-ac- quired pneumonia. Klebsiella pneumoniae This enteric is encapsulated (0 antigen) but is non- motile (no H antigen). Klebsiella pneumoniae prowls hospitals, causing sepsis (second most common after Escherichia coli). It also causes urinary tract infections in hospitalized patients with Foley catheters. Hospital- ized patients and alcoholics (debilitated patients) are prone to a Klebsiella pneumoniae pneumonia, which is characterized by a bloody sputum in about 50% of Figure 9-2 cases. This pneumonia is violent and frequently de-cause diarrhea indistinguishable from shigellosis and stroys lung tissue, producing cavities. Thick sputumcholera. The big picture here is that the different types coughed up with Klebsiella pneumoniae classicallyof diarrhea produced by Escherichia coli and the other looks like red currant jelly, which is the color of the 0enterics are dependent on virulence acquisition from antigen capsule. The mortality rate is high despite an-plasmids, and there is active sharing of these factors. So tibiotic therapy.Escherichia coli diarrhea can look just like cholera (rice-water stools) or just like shigellosis (diarrhea with bloodand white cells). Proteus mirabilis This organism is very motile. In fact, when you smearEscherichia coli Urinary Tract the bacteria on a plate it will grow not as distinct roundInfections (UTIs) colonies, but rather as a confluence of colonies as the The acquisition of a pili virulence factor allows Es- bacteria rapidly move and cover the plate. This organ- ism is able to break down urea and is thus often referred cherichia coli to travel up the urethra and infect the to as the urea-splitting Proteus. bladder (cystitis) and sometimes move further up to in- fect the kidney itself ( pyelonephritis). Escherichia coli There are 3 strains of Proteus that have cross-reacting is the most common cause of urinary tract infections, antigens with some Rickettsia ( Chapter 12, Fig. 12-11). which usually occur in women and hospitalized patients They are OX-19, OX-2, and OX-K. This is purely coinci-with catheters in the urethra. Symptoms include burn- dental but serves as a useful clinical tool to determinei ng on urination ( dysuria), having to pee frequently if a person has been infected with Rickettsia. Serum is mixed with these Proteus strains to determine( frequency), and a feeling of fullness over the bladder.Culture of greater than 100,000 colonies of bacteria whether there are antibodies in the serum that reactfrom the urine establishes the diagnosis of a urinary with the Proteus antigens. If these antibodies are pre- sent, this suggests that the patient has been infectedtract infection. with Rickettsia. Proteus is another common cause of urinary tract in-Escherichia coli Meningitis fections and hospital-acquired (nosocomial) infections. Escherichia coli is the second most common cause of Examination of the urine will reveal an alkaline pH,neonatal meningitis (group B streptococcus is first). which is due to Proteus ability to split urea into NH3During the first month of life, the neonate is especially and CO2.susceptible. EnterobacterEscherichia coli Sepsis This highly motile gram-negative rod is part of the Escherichia coli is also the most common cause of normal flora of the intestinal tract. It is occasionally re-gram-negative sepsis. This usually occurs in debilitated sponsible for hospital-acquired infections. 57
  • 64. CHAPTER 9. THE ENTERICSSerratia Serratia is notable for its production of a bright redpigment. It can cause urinary tract infections, woundinfections, or pneumonia.Shigella There are four species of Shigella (dysenteriae, flexneri, boydii, and sonnei) and all are nonmotile. If you look back at the picture of Escherichia coli and Shigella holding hands ( Fig. 9-2), you will see that Shigella has no flagella. Shigella does not ferment lac- tose and does not produce H2S. These properties can be used to distinguish Shigella from Escherichia coli (lac- tose fermenter) and Salmonella (non-lactose fermenter, produces H2S). Humans are the only hosts for Shigella, and the dysentery that it causes usually strikes preschool agechildren and populations in nursing homes. Trans-mission by the fecal-to-oral route occurs via fecallycontaminated water and hand-to-hand contact (Em-ployees please wash hands!). Shigella is never con-sidered part of the normal intestinal flora! It is always Figure 9-3a pathogen. Shigella is similar to enteroinvasive Escherichia coli( EIEC) in that they both invade intestinal epithelial Salmonellacells and release Shiga toxin, which causes cell de- ("The Salmon")struction. White cells arrive in an inflammatory reac-tion. The colon, when viewed via colonoscopy, has Salmonella is a non-lactose fermenter, is motile (likeshallow ulcers where cells have sloughed off. The illness a salmon), and produces H2S.begins with fever (unlike ETEC and cholera, which do You will hear of Salmonellas Vi antigen. This is anot invade epithelial cells and therefore do not induce polysaccharide capsule that surrounds the O anti-a fever), abdominal pain, and diarrhea. The diarrhea gen, thus protecting the bacteria from antibody attackmay contains flecks of bright-red blood and pus (white on the O antigen. This is just like the K antigen (just tocells). Patients develop diarrhea because the inflamed confuse you!), but with Salmonella they named it Vicolon, damaged by the Shiga toxin, is unable to reabsorb (for virulence).fluids and electrolytes. There are thousands of Salmonella serotypes, but clinically they are usually divided into three groups: Salmonella typhi, Salmonella cholerae-suis, and Sal-Fig. 9-3. Visualize Shazam Shigella with his Shiga monella enteritidis. This will not be that difficult to re-blaster laser, entering the intestinal epithelial cells and member because they are named according to theblasting away at the 60S ribosome, causing epithelial diseases they cause.cell death. Salmonella differs from the other enterics because it lives in the gastrointestinal tracts of animals and in- fects humans when there is contamination of food or wa-Shiga Toxin ter with animal feces. This is the same toxin as in EHEC and EIEC, and itsmechanism is the same. There is an A subunit bound to Fig. 9-4. Many animals can carry Salmonella. (Pic-5 B subunits. The B subunits (B for Binding) bind to the ture a salmon.) In the U.S. there was even an epidemicmicrovillus membrane in the colon, allowing the entry of salmonellosis from pet turtles. Today in the U.S., Sal-of the deadly A subunit (A for Action). The A subunits monella is most commonly acquired from eating chick-inactivate the 60S ribosome, inhibiting protein synthe- ens and uncooked eggs. Salmonella typhi is ansis and killing the intestinal epithelial cell. exception as it is not zoonotic (an infectious disease of 58
  • 65. CHAPTER 9. THE ENTERICS Figure 9-4 animals that can be transmitted to man). Salmonella ty- exposure and includes fever, headache, and abdominalphi is carried only by humans. pain that is either diffuse or localized to the right lower quadrant (over the terminal ilium), often mimicking ap- Salmonella (like Shigella) is never considered part of pendicitis. As inflammation of the involved organs oc-the normal intestinal flora! It is always pathogenic and curs, the spleen may enlarge and the patient maycan cause 4 disease states in humans: 1) the famous ty- develop diarrhea and rose spots on the abdomen-aphoid fever, 2) a carrier state, 3) sepsis, and 4) gas- transient rash consisting of small pink marks seen onlytroenteritis (diarrhea). on light-skinned people. Diagnose this infection by culturing the blood, urine, or stool. Ciprofloxacin or ceftriaxone are consideredTyphoid Fever This illness caused by Salmonella typhi is also called appropriate therapy.enteric fever. Salmonella typhi moves one step beyondEIEC and Shigella. After invading the intestinal ep-ithelial cells, it invades the regional lymph nodes, fi-nally seeding multiple organ systems. During thisinvasion the bacteria are phagocytosed by monocytesand can survive intracellularly. So Salmonella typhi isa facultative intracellular parasite (see Fig. 2-7).Fig. 9-5. Typhoid fever, caused by Salmonella typhi,depicted by a Salmon with fever (thermometer) and rosespots on its belly. Salmonellosis starts 1-3 weeks after Figure 9-5 59
  • 66. CHAPTER 9. THE ENTERICSCarrier StateFig. 9-6. Some people recovering from typhoid feverbecome chronic carriers, harboring Salmonella typhi intheir gallbladders and excreting the bacteria con-stantly. These people are not actively infected and donot have any symptoms. A famous example occurred in1868 when Typhoid Mary, a Swiss immigrant whoworked as a cook, spread the disease to dozens in NewYork City. (Again-employees please wash hands afterusing the toilet!) Some carriers actually require surgicalremoval of their gallbladders to cure them.SepsisFig. 9-7. Salmon cruising in the bloodstream to infectlungs, brain, or bone. This systemic dissemination isusually caused by Salmonella choleraesuis and does notinvolve the GI tract. A pearl of wisdom: Remember that Salmonella is encapsulated with the Vicapsule. Our immune system clears encapsulated bacte-ria by opsonizing them with antibodies (see Fig2-5), and then the macrophages and neutrophils in the Figure 9-6spleen (the reticulo-endothelial system) phagocytose theopsonized bacteria. So, patients who have lost theirspleens (asplenic), either from trauma or from sickle-cell Diarrhea (Gastroenteritis)disease, have difficulty clearing encapsulated bacteriaand are more susceptible to Salmonella infections. Pa- Fig. 9-8. Salmonella diarrhea is the most commontients with sickle-cell anemia are particularly type of Salmonella infection and can be caused by anyprone to Salmonella osteomyelitis (bone infection). of hundreds of serotypes of Salmonella enteritidis. The presentation includes nausea, abdominal pain, and di- Vigorous and prolonged antibiotic therapy is required arrhea that is either watery or, less commonly, containsto treat Salmonella osteomyelitis. mucous and trace blood. Fever occurs in about half theFigure 9-7 60
  • 67. CHAPTER 9. THE ENTERICS Figure 9-Spatients. This diarrhea is caused by a yet-uncharacter- ally an enteric bacterium but is included here becauseized cholera-like toxin (watery diarrhea) and sometimes it causes diarrhea. This organism is closely related toalso by ileal inflammation (mucous diarrhea). Yersinia pestis, which is the cause of the bubonic plague. Like Yersinia pestis, animals are a major source of Treatment usually involves only fluid and electrolyte Yersinia enterocolitica; Yersinia enterocolitica differs inreplacement, as antibiotics do not shorten the course of that it is transferred by the fecal-oral route rather thanthe disease and do cause prolonged bacterial shedding the bite of a flea.i n the stool. The diarrhea only lasts a week or less. Following ingestion of contaminated foods, such as milk from domestic farm animals or fecally contami-Yersinia enterocolitica nated water, patients will develop fever, diarrhea, and abdominal pain. This pain is often most severe in the This motile gram-negative rod is another cause of right lower quadrant of the abdomen, and therefore pa-acute gastroenteritis. Since entero is part of Yersinia tients may appear to have appendicitis. Examination ofenterocoliticas name, it is not surprising that this or- the terminal ileum (located in the right lower quadrant)ganism is a cause of acute gastroenteritis. It is not re- will reveal mucosal ulceration. 61
  • 68. CHAPTER 9. THE ENTERICS The pathogenesis of this organism is twofold: there is no epithelial cell invasion. The bacteria attach to the epithelial cells and release the cholera toxin, 1) Invasion: Like Salmonella typhi, this organism which is called choleragen. The disease presents withpossesses virulence factors that allow binding to the in- the abrupt onset of a watery diarrhea (classically de-testinal wall and systemic invasion into regional lymph scribed as looking like rice water) with the loss of upnodes and the bloodstream. Mesenteric lymph nodes to 1 liter of fluid per hour in severe cases. Shock fromswell, and sepsis can develop. isotonic fluid loss will occur if the patient is not rehy- 2) Enterotoxin: This organism can secrete an en- drated. Like ETEC:terotoxin, very similar to the heat-stable enterotoxin ofEscherichia coli, that causes diarrhea. Cholera causes death by dehydration. Diagnosis can be made by isolation of this organism Physical findings such as diminished pulses, sunkenfrom feces or blood. Treatment does not appear to alter eyes, and poor skin turgor will develop with severe de-the course of the gastroenteritis, but patients who have hydration.sepsis should be treated with antibiotics. Although re-frigeration of food can wipe out many types of bacterial Choleragenpathogens, Yersinia enterocolitica can survive and growin the cold. This toxin has the same mechanism of action as Es- Other members of the Enterobacteriaceae family that cherichia colis LT toxin (although choleragen is codedyou will hear of on the wards include Edwardsiella, Cit- on the chromosome, while LT is transmitted via a plas-robacter, Hafnia, and Providencia. mid). There is one A subunit (Action) attached to five B subunits (Binding). The B subunit binds to the GM1 ganglioside on the intestinal epithelial cell surface, al- FAMILY VIBRIONACEAE lowing entry of the A subunit. In the cell, the A subunit activates G-protein, which in turn stimulates the activ-Vibrio cholera ity of a membrane-bound adenylate cyclase, resulting in the production of cAMP. Intracellular cAMP results in active secretion of Na and Cl as well as the inhibition of Na and Cl reabsorption. Fluid, bicarbonate, and potas- sium are lost with the osmotic pull of the NaCl as it trav- els down the intestine. Microscopic exam of the stool should not reveal leukocytes (white cells) but may reveal numerous curved rods with fast darting movements. Treatment with fluid and electrolytes is lifesaving, and doxycycline will shorten the duration of the illness. Vibrio parahaemolyticus This organism is a marine bacterium that causes gas-Figure 9-9 troenteritis after ingestion of uncooked seafood (sushi).Fig. 9-9. As you can see, Vibrio cholera is a curved This organism is the leading cause of diarrhea in Japan.gram-negative rod with a single polar flagellum. Cholera is the diarrheal disease caused by Vibrio Campylobacter jejunicholera. The bacteria are transmitted by the fecal-oralroute, and fecally contaminated water is usually the (Camping bacteria in the jejunum with nothing bet-culprit. Adults in the U.S., especially travelers, and ter to do than cause diarrhea!)children in endemic areas are the groups primarily in-fected (immunity develops in adults in endemic areas). This critter is important!!! This gram-negative rodRecent epidemics have arisen secondary to poor dis- that looks like Vibrio cholera (curved with a single po-posal of sewage in many South American countries lar flagellum) is often lost deep in textbooks. Dont let(400,000 cases in Latin America in 1991), and 1993 this happen. Campylobacter jejuni, ETEC, and the Ro-monsoon floods that mixed feces with potable water in tavirus are the three most common causes of diarrheaBangladesh. in the world. Estimates are that Campylobacter jejuni The bacteria multiply in the intestine and cause the causes up to 2 million cases of diarrhea a year in thesame disease as ETEC, but more severe. As with ETEC, U.S. alone. 62
  • 69. CHAPTER 9. THE ENTERICS This is a zoonotic disease, like most Salmonella (except 2) The rascal is resistant to almost every antibiotic, Salmonella typhi), with reservoirs of Campylobacter je- so it has become an art to think up "anti-pseudomonal juni in wild and domestic animals and in poultry. The fe- coverage." Drug salesmen will always mention the cov- caloral route via contaminated water is often the mode erage for Pseudomonas. of transmission. This organism can also be acquired by drinking unpasteurized milk. As with most diarrheal ill- Pseudomonas aeruginosa is an obligate aerobic (non- ness, children are the most commonly affected worldwide. lactose fermenter), gram-negative rod. It produces a The illness begins with a prodrome of fever and green fluorescent pigment (fluorescein) and a blue pig- headache, followed after half a day by abdominal cramps ment (pyocyanin), which gives colonies and infected and a bloody, loose diarrhea. This organism invades the wound dressings a greenish-blue coloration. It also pro- lining of the small intestine and spreads systemically as duces a sweet grape-like scent, so wound dressings and do Salmonella typhi and Yersinia enterocolitica. Campy- agar plates are often sniffed for organism identification. lobacterjejuni also secretes an LT toxin similar to that Pseudomonas aeruginosa has weak invasive ability. of Escherichia coli and an unknown cytotoxin that de- Healthy people just dont get infections with this guy! stroys mucosal cells. However, once inside a weakened patient, the story Helicobacter pylori changes. It elaborates numerous exotoxins including exotoxin A, which has the same mechanism of action (formerly called Campylobacter pylori) as diphtheria toxin (stops protein synthesis) but is not antigenically identical. Some strains also possess a cap- This organism is the most common cause of duo- sule that is antiphagocytic and aids in adhesion to tar- denal ulcers and chronic gastritis (inflamed stomach). get cells (in the lungs for example). (Aspirin products rank second.) It is the second leading cause of gastric (stomach) ulcers, behind aspirin prod- ucts. The evidence for this is as follows: Important Pseudomonas aeruginosa Infections 1) Helicobacter pylori can be cultured from ulcercraters. 1) Pneumonia (see Fig. 16-5) 2) Feeding human volunteers Helicobacter pylori a) Most cystic fibrosis patients have their lungs colonized with Pseudomonas aeruginosa. These pa- 3) Pepto-Bismol, used for years for gastritis, has bis-causes ulcer formation and gastritis. tients develop a chronic pneumonia, which progres-muth salts, which inhibit the growth of Helicobacter pylori. sively destroys their lungs. 4) Antibiotics help treat duodenal and gastric ulcer b) Immunocompromised patients (cancer pa-disease: Multiple recent studies have shown that treat- tients and intensive care unit patients) are highlyment with combinations of bismuth salts, Metronida- susceptible to pneumonia caused by Pseudomonaszole, ampicillin, and/or tetracycline, clears Helicobacter aeruginosa.pylori and results in a dramatic decrease in both duo- 2) Osteomyelitisdenal and gastric ulcer recurrence (Veldhuyzen van a) Diabetic patients have an increased risk of de-Zanten, 1994; Ransohoff, 1994; Sung, 1995). veloping foot ulcers infected with Pseudomonas aeruginosa. The infection can penetrate into theFig. 9-10. Helicobacter pylori causes duodenal and bone resulting in osteomyelitis.gastric ulcers and gastritis. Visualize a Helicopter- b) Intravenous (IV) drug abusers have an in-bacteria lifting the cap off a duodenal and gastric ulcer creased risk of osteomyelitis of the vertebrae orcrater. If you have a more violent disposition, visualize Apache helicopter-bacteria shooting hellfire mis- c) Children develop osteomyelitis secondary tosiles at the stomach. puncture wounds to the foot. FAMILY PSEUDOMONADACEAE 3) Burn-wound infections: This organism sets up significant infections of burn wounds, which eventuallyPseudomonas aeruginosa lead to a fatal sepsis. 4) Sepsis: Pseudomonas sepsis carries an extremely You are going to hear so much about this bug while high mortality rate.working in the hospital that you will wish the Lord had 5) Urinary tract infections, pyelonephritis: Thisnever conjured it up. There are two reasons why it is so occurs in debilitated patients in nursing homes and inimportant: hospitals. They often have urethral Foley catheters, which serve as a source of infection. 1) It colonizes and infects sick, immunocompromised 6) Endocarditis: Staphylococcus aureus and Pseudo-hospitalized patients, the kind of patient you will take monas aeruginosa are frequent causes of right heartcare of in the hospital. valve endocarditis in IV drug abusers. 63
  • 70. CHAPTER 9. THE ENTERICS Figure 9-10 7) Malignant external otitis: A Pseudomonas ex-ternal ear canal infection burrows into the mastoid FAMILY BACTEROIDACEAEbone, primarily in elderly diabetic patients. We have spent so much time studying all the preced- 8) Corneal infections: This can occur in contact ing enteric bacteria that you may be surprised to findlens wearers. out that 99% of the flora of our intestinal tract is made up of obligate anaerobic gram-negative rods comprising Treatment of Pseudomonas is complicated as it is re- the family Bacteroidaceae. The mouth and vagina aresistant to many antibiotics. Chapter 16, Fig. 16-14, lists also home to these critters.all the antibiotics used to treat Pseudomonas. An anti-pseudomonal penicillin is usually combined with anaminoglycoside for synergy (for example, piperacillin Bacteroides fragilisand gentamicin). This bacterium is notable for being one of the few Pseudomonas cepacia is rapidly becoming an im- gram-negative bacteria that does not contain lipid A inportant pathogen, infecting hospitalized patients (burn its outer cell membrane (NO endotoxin!). However, itand cystic fibrosis patients) in a similar manner. does possess a capsule. 64
  • 71. CHAPTER 9. THE ENTERICS You will become very familiar with Bacteroides frag- Fusobacterium ilis while studying surgery. This bacterium has low vir- ulence and normally lives in peace in the intestine. This bacterium is just like Bacteroides melaninogeni- However, when a bullet tears into the intestine, when a cus in that it also causes periodontal disease and aspi- seat belt lacerates the intestine in a car wreck, when ab- ration pneumonias. Fusobacterium can also cause dominal surgery is performed with bowel penetration, abdominal and pelvic abscesses and otitis media. or when the intestine ruptures secondary to infection (appendicitis) or ischemia, THEN the bacteria go wild in ANAEROBIC GRAM-POSITIVE COCCI the peritoneal cavity, forming abscesses. An abscess is Peptostreptococcus (strip or chain of cocci) and Pepto- a contained collection of bacteria, white cells, and dead coccus (cluster of cocci) are gram-positive anaerobes tissue. Fever and sometimes systemic spread accom- that are part of the normal flora of the mouth, vagina, pany the infection. and intestine. They are mixed with the preceding or- Phis abscess formation is also seen in obstetric and ganisms in abscesses and aspiration pneumonias. gynecologic patients. Abscesses may arise in a patient Members of the Streptococcus viridans group, dis- with a septic abortion, pelvic inflammatory disease cussed in Chapter 4, are mentioned here because they (tubo-ovarian abscess), or an intrauterine device (IUD) are gram-positive, microaerophilic, and are frequently for birth control. isolated from abscesses (usually mixed with other anaer- Bacteroides fragilis is rarely present in the mouth, so obic bacteria). These oxygen-hating critters have manyit is rarely involved in aspiration pneumonias. names (such as Streptococcus anginosus and Streptococ- Following abdominal surgery, antibiotics that cover cus milleri) and are a part of the normal GI flora.anaerobes are given as prophylaxis against Bacteroidesfragilis. These include clindamycin, metronidazole Fig. 9-11. Summary of enteric bacteria.(Flagyl), chloramphenicol, and others (see Chapter 16,Fig. 16-15). If an abscess forms, it must be surgically Referencesdrained. Veldhuyzen van Zanten SF, Sherman PM. Helicobacter pylori infection as a cause of gastritis, duodenal ulcer, gastric can-Bacteroides melaninogenicus cer and nonulcer dyspepsia: a systematic overview. Can Med Assoc F 1994;150:177-185. This organism produces a black pigment when grown Veldhuyzen van Zanten SF, Sherman PM. Indications foron blood agar. Hence, the name melaninogenicus. It treatment of Helicobacter pylori infection: a systematic overview. Can Med Assoc F 1994;150:189-198.lives in the mouth, vagina, and intestine, and is usually Ransohoff DF. Commentary. ACP Journal Club 1994; 120:involved in necrotizing anaerobic pneumonias caused aspiration of lots of sputum from the mouth (during Sung, JY, et al. Antibacterial treatment of gastric ulcers asso-a seizure or drunken state). It also causes periodontal ciated with Helicobacter pylori. New Engl J Med 1995;332:disease. 139-42. 65
  • 72. M. Gladwin and B. Trattler, Clinical Microbiology Made Ridiculously Simple ©MedMasterFigure 9-11 (continued)
  • 73. CHAPTER 10. HAEMOPHILUS, BORDETELLA, and LEGIONELLAThe gram-negative rods Haemophilus influenzae, Borde- Haemophilus influenzae type btella pertussis and Legionella pneumophila are groupedtogether because they are all acquired through the respi- 1) Meningitis: This is the most serious infectionratory tract. This makes sense if you consider the species caused by encapsulated Haemophilus influenzae type b.names: influenzae (the flu-an upper respiratory ill- Prior to the introduction of vaccination of U.S. childrenness),pertussis (cough), and pneumophila (lung loving). in 1991, it was the main cause of meningitis in young children between the age of 6 months to 3 years (moreHaemophilus influenzae than 10,000 cases per year). Following inhalation, this organism invades the local lymph nodes and blood- The name Haemophilus influenzae describes some of stream, and then penetrates into the meninges. Sinceits properties: infants usually do not display the classic stiff neck, non- Haemophilus means "blood loving." This organism specific signs such as fever, vomiting, and altered men-requires a blood-containing medium for growth. Hema- tal status are the clues to this potentially fatal infection.tin found in blood is necessary for the bacteriums cy- Although mortality with appropriate antibiotics istochrome system. Blood also contains NAD, needed for less than 5%, up to half of infected children will stillmetabolic activity. have permanent residual neurologic deficits, such as influenzae: This bacterium often attacks the lungs mental retardation, seizures, language delay, or deaf-of persons debilitated by a viral influenza infection. ness. When a bacterial meningitis is treated with an-During the 1890 and 1918 influenza pandemics, scien- tibiotics, the killed bacteria lyse and release cellulartists cultured Haemophilus influenzae from the upper antigens, such as LPS lipid A (endotoxin), resulting in arespiratory tracts of "flu" patients, leading them to in- violent immune response that destroys neurons as wellcorrectly conclude that Haemophilus influenzae was the as bacteria. Recent studies show that treatment withetiologic agent of the flu. steroids 15-20 minutes before giving N antibiotics will Haemophilus influenzae is an obligate human para- decrease this risk of developing neurologic deficits. It issite that is transmitted via the respiratory route. Two theorized that the steroids limit the inflammatory re-important concepts help us understand how this crittercauses disease: sponse to the dead bacterias antigens while allowing bacterial killing. 1) A polysaccharide capsule confers virulence: There 2) Acute epiglottitis: Haemophilus influenzae typeare 6 types of capsules, designated a, b, c, d, e, and f. Of b can also cause rapid swelling of the epiglottis, ob-these, type b is commonly associated with invasive structing the respiratory tract and esophagus. Follow-Haemophilus influenzae disease in children, such as ing a sore throat and fever, the child develops severemeningitis, epiglottitis, and septic arthritis. upper airway wheezing (stridor) and is unable to swal- low. Excessive saliva will drool out of the childs mouth Capsule b = bad as it is unable to pass the swollen epiglottis. The large, Nonencapsulated strains of Haemophilus influenzae red epiglottis looks like a red cherry at the base of the can colonize the upper respiratory tract of children and tongue. If you suspect this infection, do not examine the adults. They lack the virulent invasiveness of their en- larynx unless you are ready to insert an endotracheal capsulated cousins and can only cause local infection. breathing tube because manipulation can cause laryn- They frequently cause otitis media in children as well as geal spasm. This may cause complete airway obstruc- respiratory disease in adults weakened by preexisting tion that can only be bypassed with a tracheotomy. lung disease, such as chronic bronchitis from smoking 3) Septic arthritis: Haemophilus influenzae type bor recent viral influenza infection. is the most common cause of septic arthritis in infants. Most commonly, a single joint is infected, resulting in fever, pain, swelling and decreased mobility of the joint. 2) Antibodies to the capsule are lacking in infants Examination of the synovial fluid (joint fluid) by Gramand children between 6 months and 3 years of age. The stain reveals the pleomorphic gram-negative rods.mother possesses antibodies against the b capsule 4) Sepsis: Children between 6 months to 3 years pre-which she has acquired in her lifetime. She passes theseantibodies to the fetus transplacentally and in herbreast milk. These "passively" acquired antibodies last sent with fever, lethargy, loss of appetite, and no evi- dence of localized disease (otitis media, meningitis, or epiglottitis). Presumably the bacteria invade the blood-for about 6 months. It takes 3-5 years of Haemophilus stream via the upper respiratory tract. Since the spleeninfluenzae colonization and infection for children to de- is the most important organ in fighting off infection byvelop their own antibodies. So there is a window during encapsulated bacteria, it is not surprising that childrenwhich children are sitting ducks for the invasiveHaemophilus influenzae. 68
  • 74. CHAPTER 10. HAEMOPHILUS, BORDETELLA, AND LEGIONELLA with absent or non-functioning spleens (either by 2) Herpes ( Herpes simplex virus 1 and 2): Herpetic surgery or with sickle-cell disease) are at highest risk. lesions start as vesicles (blisters), yet once they break Prompt identification and treatment will prevent they can be misdiagnosed as chancroid, especially be- Haemophilus influenzae type b from invading the cause they are painful. Herpes is usually accompanied meninges, epiglottis, or a joint. by systemic symptoms such as myalgias and fevers. Meningitis, epiglottitis, and bacterial sepsis are Chancroid does not usually produce systemic symptoms. rapidly fatal without antibiotic therapy. Ampicillin 3) Lymphogranuloma venereum (Chlamydia tra- used to be the drug of choice prior to the development of chomatis): LGV has painless matted suppurative in- resistance. Ampicillin resistance is transmitted by a guinal lymph nodes that develop much more slowly plasmid from strain to strain of Haemophilus influen- than chancroid. The primary ulcer of LGV disappears zae. Currently, a third generation cephalosporin, such before the nodes enlarge, whereas with chancroid they as cefotaxime or ceftriaxone, is the drug of choice for coexist. serious infections. Ampicillin or amoxicillin can be used for less serious infections, such as otitis media. Treat chancroid with erythromycin or trimetho- prim/sulfamethoxazole. Effective treatment of geni- tal ulcers is crucial, because these open lesions create a Vaccination break in the skin barrier, increasing the risk of HIV ( Hib capsule vaccine) transmission. The key to controlling this organism is to stimulate Gardnerella vaginalis the early generation of protective antibodies in young children. However, it is difficult to stimulate antibody (formerly Haemophilus vaginalis) formation in the very young. This organism causes bacterial vaginitis in conjunc- The first vaccine, consisting of purified type b cap- tion with anaerobic vaginal bacteria. Women with sule, was effective only in generating antibodies in chil- vaginitis develop burning or pruritis (itching) of the dren older than 18 months. A second new vaccine is labia, burning on urination (dysuria), and a copious, composed of the Haemophilus influenzae type b (Hib) foul-smelling vaginal discharge that has a fishy odor. It capsule and diphtheria toxin. The addition of the diph- can be differentiated from other causes of vaginitis theria toxin activates T-lymphocytes and antibodies (such as Candida or Trichomonas) by examining a slide against the b capsule. Vaccination with the Hib capsule of the vaginal discharge (collected from the vagina dur- of children in the U.S. at ages 2, 4, 6, and 15 months ing speculum exam) for the presence of clue cells. Clue (along with the DTP and polio vaccines) has dramati- cells are vaginal epithelial cells that contain tiny pleo- cally reduced the incidence of Haemophilus influenzae morphic bacilli within the cytoplasm. infection. Acute Haemophilus influenzae epiglottitis is Treat this infection with metronidazole, which cov- now rarely seen in U.S. emergency rooms. ers Gardnerella as well as co-infecting anaerobes. As a note, this species was separated from the genus Hib, Hib, Hurray! Haemophilus because it does not require X-factor or V- Other efforts involve immunizing women in the factor for growth in culture. Bordetella pertussiseighth month of pregnancy, resulting in increased anti-body secretion in breast milk (passive immunization).Haemophilus ducreyi This bacterium is named: Bordetella because it was discovered in the early 1900s by two scientists named Bordet and Gengou. It This species is responsible for the sexually transmitted seems that Bordet got the better end of the deal!disease chancroid. Clinically, patients present with a Pertussis means "violent cough." Bordetella pertus-painful genital ulcer. Unilateral painful swollen in- sis causes whooping cough.guinal lymph nodes rapidly develop in half of infectedpersons. The lymph nodes become matted and will rup- Exotoxin Weaponsture, releasing pus. The differential diagnosis includes: Bordetella pertussis is a violently militant critter with a (gram) negative attitude. He is a gram-negative 1) Syphilis ( Treponema pallidum): It is extremely rod armed to the hilt with 4 major weapons (virulenceimportant to exclude syphilis as the cause of the ulcer. factors). These virulence factors allow him to attach toRemember that the ulcer of syphilis is painless and the the ciliated epithelial cells of the trachea and bronchi.associated adenopathy is bilateral, painless, and non- He evades the hosts defenses and destroys the ciliatedsuppurative (no pus). cells, causing whooping cough. 69
  • 75. CHAPTER 10. HAEMOPHILUS, BORDETELLA, AND LEGIONELLA 1) Pertussis toxin: Like many bacterial exotoxins hands or in an aerosolized form. A week-long incubation this toxin has a B subunit that Binds to target cell re- period is followed by 3 stages of the disease: ceptors, "unlocks" the cell, allowing entry of the A sub- unit. The A subunit (A for Action) activates 1) Catarrhal stage: This stage lasts from 1-2 weeks cell-membrane-bound G regulatory proteins, which in and is similar to an upper respiratory tract infection, withturn activate adenylate cyclase. This results in an out- low-grade fevers, runny nose, sneezing, and mild cough.pouring of cAMP, which activates protein kinase and It is during this period that the disease is most contagious. 2) Paroxysmal stage: The fever subsides and theother intracellular messengers. The exact role of thistoxin in whooping cough is not entirely clear, but it has infected individual develops characteristic bursts of3 observed effects: a) histamine sensitization, b) in- nonproductive cough. There may be 15-25 of these at-crease in insulin synthesis, and c) promotion of lympho- tacks per day, and the person may appear normal be-cyte production and inhibition of phagocytosis. tween events. The attacks consist of 5-20 forceful 2) Extra cytoplasmic adenylate cyclase: When coughs followed by an inspiratory gasp through the nar-attacking the bronchi, Bordetella pertussis throws its rowed glottis. This inspiration sounds like a whoop.adenylate cyclase grenades. They are swallowed by host During these paroxysms of coughing the patient can be-neutrophils, lymphocytes, and monocytes. The internal- come hypoxemic and cyanotic (blue from low oxygen),ized adenylate cyclase then synthesizes the messenger the tongue may protrude, eyes bulge, and neck veins en-cAMP, resulting in impaired chemotaxis and impaired gorge. Vomiting often follows an attack. The paroxys-generation of H2O2 and superoxide. This weakens the mal stage can last a month or longer. The illness is morehost defense cells ability to phagocytose and clear the severe in the young, with up to 75% of infants less thanbacteria. 6 months of age and 40% of infants and young children 3) Filamentous hemagglutinin (FHA): Bordetella more than 6 months requiring hospitalization.pertussis does not actually invade the body. It attaches Infants and partially immunized (wearing off) chil-to ciliated epithelial cells of the bronchi and then re- dren and adults may not have the typical whoop. In-leases its damaging exotoxins. The FHA, a pili rod ex- fants can have cough and apnea spells (no breathing).tending from its surface, is involved in this binding. Adults may present with a persistent cough.Antibodies directed against the FHA prevent binding Examination of the white blood cells will surprisinglyand disease, and thus they are protective. reveal an increase in the lymphocyte count with just a 4) Tracheal cytotoxin: This toxin destroys the cili- modest increase in the neutrophils (more like a viral pic-ated epithelial cells, resulting in impaired clearance of ture). The increased number of lymphocytes seems to bebacteria, mucus, and inflammatory exudate. This toxin one of the manifestations of the pertussis probably responsible for the violent cough. 3) Convalescent stage: The attacks become less frequent over a month, and the patient is no longer con- tagious.Whooping Cough Since this organism will not grow on cotton, speci- The number of cases of whooping cough has decreased dramatically since vaccination programs began. In the mens for culture are collected from the posterior phar- ynx with a calcium alginate swab. This swab is prevaccination era in the United States, there were ap- i nserted into the posterior nares and the patient is then proximately 100-300 thousand cases a year, and now only 1-4 thousand!!! Prior to the development of the vac- instructed to cough. The swab is then wiped on a special cine, children between the ages of 1-5 were most likely culture medium with potato, blood, and glycerol agar, called the Bordet-Gengou medium. At most hospi- to catch this disease. The majority of cases today occur in unimmunized in- tals, identification of this bacterium can be made with fants younger than 1 year. Infants younger than 6 rapid serological tests (ELISA). months used to be protected by maternal antibodies Treatment is primarily supportive. Infants are hospi- that crossed the placenta during pregnancy. However, talized to provide oxygen, suctioning of respiratory secre-the vaccine only provides a high level of protective anti- tions, respiratory isolation, and observation. Treatmentbodies during the first 15 years of life, so most mothers of infected individuals with erythromycin in the pro-do not have protective antibodies to pass to their in- dromal or catarrhal stage may prevent the disease. Laterfants. Therefore, unimmunized infants under 1 year are therapy during the paroxysmal stage does not alter thevery susceptible to this infection today. Since the vac- course of illness but may decrease bacterial shedding.cine only provides immunity for approximately 15 Household contacts should receive erythromycin also.years, young adults are another group that is currently Vaccinationat a higher risk for acquiring whooping cough. Whooping cough is a highly contagious disease with The vaccine currently used in the U.S. consists oftransmission occurring via respiratory secretions on the heat-killed organisms and includes the pertussis toxin, 70
  • 76. CHAPTER 10. HAEMOPHILUS, BORDETELLA, AND LEGIONELLA FHA, and adenylate cyclase. It is combined with the for- tiac fever to a severe pneumonia called Legionnaires malin inactivated tetanus and diphtheria toxoids to disease: form the DPT (Diphtheria-Pertussis-Tetanus) vaccine, and is given at 2, 4, 6, and 15-18 months of age. This 1) Pontiac fever: Like influenza, this disease in- vaccine has been very effective in reducing the number volves headache, muscle aches, and fatigue, followed by fever and chills. Pontiac fever strikes suddenly andof whooping cough cases but carries a price. Infants may develop side effects such as local swelling and pain and completely resolves in less than one week. Pontiac fever was so-named for the illness that struck 95% of systemic fever, persistent crying, and, rarely, limpness the employees of the Pontiac, Michigan, County (hypotonicity) and seizures. In efforts to reduce these adverse effects new vaccines Health Department. The causative agent was identi- have been developed that are composed only of inacti- fied as Legionella pneumophila carried by the air con- vated proteins such as pertussis toxin, FHA, and others ditioning system. (such as pertactin and fimbrial antigens). In two recent 2) Legionnaires disease: Patients develop very large studies, these vaccines were found to be safer and high fevers and a severe pneumonia. Legionella pneumophila is one of the most common worked better than the U.S. whole-cell vaccine!!! (Greco, 1996; Gustafsson, 1996). causes of community acquired pneumonia and is esti- mated to be diagnosed correctly in only 3% of cases! It should be suspected in all patients who have pneumo- nia who are over 50 years of age and especially if theyLegionella pneumophila are smokers or if the sputum gram stain reveals neu-( Legionnaires Pneumonia) trophils and very few organisms. (Legionella is so small Legionella pneumophila is an aerobic gram-negative it is hard to see on gram stain.) rod that is famous for causing an outbreak of pneumo- Treat with erythromycin because this organism hasnia at an American Legion convention in Philadelphia a beta-lactamase making it resistant to penicillins.i n 1976 (thus its name). Then attempt to determine the source of Legionella. Is This organism is ubiquitous in natural and man- the air conditioning system contaminated? Fig. 10-1. Summary of Haemophilus, Bordetella andmade water environments. Aerosolized contaminatedwater is inhaled, resulting in infection. Sources thathave been identified during outbreaks have included air Legionella.conditioning systems, cooling towers, and whirlpools.Outbreaks have even been associated with organism Referencesgrowth in shower heads and produce mist machines insupermarkets!!! Person-to-person transmission has not Greco D, Salmaso S, et al. A controlled trial of two acellularbeen demonstrated. vaccines and one whole-cell vaccine against pertussis. N. Like Mycobacterium tuberculosis, this organism is a Eng. J. Med. 1996;334:341-8.facultative intracellular parasite that settles in the Gustafsson L, Hollander H0, et al. A controlled trial of a two-lower respiratory tract and is gobbled up by macro- component acellular, a five-component acellular, and a whole-cell pertussis vaccine. N. Eng. J. Med. 1996;334:349-phages. This means that once it has been phagocytosed, inhibits phagosome-lysosome fusion, surviving and Hewlett EL. Bordetella species. In: Mandell GL, Bennett JE,replicating intracellularly. Dolin R. Editors. Principles and Practice of Infectious Dis- Legionella is responsible for diseases ranging from eases. 4th edition. New York: Churchill Livingstoneasymptomatic infection and a flulike illness called Pon- 1995;2078-2084. 71
  • 77. Figure 10-1 HAEMOPHILUS, BORDETELLA AND LEGIONELLA M. Gladwin and B. Trattler, Clinical Microbiology Made Ridiculously Simple ©MedMaster
  • 78. CHAPTER 11. YERSINIA, FRANCISELLA, BRUCELLA, AND PASTEURELLA These organisms have been included in the same chap- 2) V and W antigens: These antigens, which are a ter because they share many characteristics (Pas- protein and lipoprotein respectively, are unique to the teurella only shares the first 2): Yersinia genus. Their actions are unknown. 1) They are all gram-negative rods (bacilli). Fig. 11-1. Visualize a rat riding in a Fuel Injected 2) All of these are zoonotic diseases (i.e., they are pri- (Fl), VW bug, being pursued by a macrophage. These marily diseases of animals). three virulence factors are involved in Yersinia pestis 3) These bacteria are very virulent and are able to resistance to destruction after phagocytosis. penetrate any body area they touch. This can occur on the skin following an insect bite, animal bite, or direct contact with an animal. This can also occur in the lungs after inhalation of infected aerosolized matter. 4) From the site of contact (usually the skin) the bac- teria are phagocytosed by macrophages. They can sur- vive inside the macrophages and so are facultative intracellular organisms. They migrate to the re- gional lymph nodes, set up infection there, and then move to the bloodstream and other organs, such as the liver, spleen, and lungs. Like other facultative intracellular organisms (seeFig. 2-7) immunity is cell-mediated, and intradermalinjections of bacterial extracts will elicit a delayed-type-hypersensitivity (DTH) reaction. This reaction resultsin skin swelling and induration (hardening) at the in-jection site 1-2 days later. The presence of swelling in- Figure 11-1dicates previous exposure to the bacteria and can be Fig. 11-2. Yersinia pestis is a gram-negative bac-used as a diagnostic test (see discussion of DTH and in- terium with a bipolar staining pattern. The ends of thetradermal skin testing in Chapter 14, page 104) rod-shaped bacterium take up more stain than the cen- 5) The common treatment is an aminoglycoside ter. Three mammals fall prey to Yersinia pestis: wild ro-(gentamicin or streptomycin) and/or doxycycline, dents, domestic city rodents, and humans. The bacteriawhich must be given for a prolonged period so as to reside in the wild rodent population between epidemicsreach the hidden intracellular bacteria. and are carried from rodent to rodent by the flea. When wild rodents come into contact with domestic city rats (during droughts when wild rodents forage for food), fleas can then carry the bacteria to domestic rats. As theYersinia pestis(Bubonic Plague) domestic rat population dies, the fleas become hungry You have all heard of bubonic plague and that rats and search out humans. were somehow involved. Rats are the PESTS (Yersiniapestis) that harbor this disease, while fleas serve as During interepidemic periods (we are in one now), vectors, carrying Yersinia pestis to humans. Bubonic bubonic plague may be contracted during camping, plague destroyed one fourth of the population of Eu- hunting or hiking. The human victim either touches arope in the 14th century. Later outbreaks moved from dead infected rodent or is bitten by an infected flea.China to India (where the disease killed 10 million) The bacteria invade the skin and are gobbled up byand in the 1900s to San Francisco. The organism now macrophages. They continue to reproduce intracellu-resides in squirrels and prairie dogs of the southwest- larly and within a week move to the nearest lymphern U. S. nodes, usually the inguinal nodes (boubon is the Greek The Fl, V, and W virulence factors enable this or- word for "groin"). The nodes swell like eggs and becomeganism to resist destruction after phagocytosis (faculta- hot, red, and painful. Fever and headache set in. Thetive intracellular organism): bacilli invade the bloodstream, liver, lungs, and other organs. Hemorrhages under the skin cause a blackish 1) Fraction 1 (Fl): This capsular antigen has an- discoloration, leading people to call bubonic plague thetiphagocytic properties. "Black Death." Without treatment, death can occur in a 73
  • 79. CHAPTER 11. YERSINIA, FRANCISELLA, BRUCELLA, AND PASTEURELLAFigure 11-2few days. During epidemics, the disease can also be seen ing rabbits, other mammals, and even reptiles and fish. as pneumonic plague with pneumonia and human-to- Tularemia is distributed all over the U.S.human transmission by aerosolized bacteria. If you see a patient who has been camping in Arizona Fig. 11-3. Francis ( Francisella) the rabbit (rabbitor New Mexico and has developed fever, have a high in- vector) is playing in the Tulips (Tularensis). One eardex of suspicion. You may want to start gentamicin has a tick, the other a deerfly.right away. You cant depend on the presence of swollenlymph nodes: Between 1980 and 1984, 25% of the cases Like Yersinia pestis, this organism is extremely viru-in New Mexico did not have lymph node involvement. lent and can invade any area of contact, resulting in This disease is deadly if untreated! About 75% of un- more than one disease presentation. The most impor-treated people die! tant diseases caused by Francisella tularensis are the Control of epidemics involves DDT for the fleas and ulceroglandular and pneumonic diseases:destruction of the rats. If you only kill the rats, thestarving fleas will feed on humans instead! 1) Ulceroglandular tularemia: Following the bite Another species of Yersinia called Yersinia enterocol- of a tick or deerfly, or contact with a wild rabbit, a well-itica infects the colon and is closely related to Es- demarcated hole in the skin with a black base develops.cherichia coli (see Chapter 9 page 61). Fever and systemic symptoms develop, and the local lymph nodes become swollen, red, and painful (some-Francisella tularensis times draining pus). The bacteria can then spread to the(Tularemia) blood and other organs. Note that these symptoms are almost identical to bubonic plague, but the skin ulcer is Tularemia is a disease that resembles bubonic plague usually absent in the plague and the mortality rate isso closely that it is always included in the differential di- not nearly as high as in bubonic plague, reaching 5% foragnosis when considering bubonic plague. This disease ulceroglandular most commonly acquired from handling infected rab- 2) Pneumonic tularemia: Aerosolization of bacte-bits and from the bites of ticks and deerflies. More ria during skinning and evisceration of an infectedthan a hundred creatures carry this bacterium, includ- rabbit or hematogenous spread from the skin (ulcerog- 74
  • 80. CHAPTER 11. YERSINIA, FRANCISELLA, BRUCELLA, AND PASTEURELLA Figure 11-3landular tularemia) to the lungs can lead to a lung in- Humans acquire Brucella from direct contact withfection (pneumonia). infected animal meat or aborted placentas, or inges- tion of infected milk products. The incidence of this dis- Francisella tularensis can also invade other areas of ease worldwide is greater than that of both buboniccontact such as the eyes (oculoglandular tularemia) plague and tularemia. In the U. S., however, it is notand the gastrointestinal tract (typhoidal tularemia). very common because cattle are immunized and milk is Because this bacterium is so virulent (just 10 organ- pasteurized.isms can cause disease), most labs will not culture it Fig. 11-4. If you do see a patient with brucellosis, hefrom blood or pus. For the same reason it is not advis- will most likely be a worker in the meat-packing indus-able to drain the infected lymph nodes. Diagnosis restson the clinical picture, a skin test similar to the PPD fortuberculosis, and the measurement of the titers of anti-bodies to Francisella tularensis.Brucella(Brucellosis) All the names of Brucella species are based on the an-imal they infect: • • Brucella melitensis (goats) • Brucella abortus (causes abortions in cows) • Brucella suis (pigs) Brucella canis (dogs) Figure 11-4 75
  • 81. CHAPTER 11. YERSINIA, FRANCISELLA, BRUCELLA, AND PASTEURELLAtry (beef), a veterinarian, a farmer, or a traveler whoconsumes dairy (cow or goat) products in Mexico or else-where. Like the other bacteria in this chapter, Brucella pen-etrates the skin, conjunctiva, lungs, or GI tract. How-ever, neither buboes nor a primary skin ulcer appear.Penetration is followed by lymphatic spread, facultativeintracellular growth in macrophages, and blood and or-gan invasion. The symptoms are systemic with fever,chills, sweats, loss of appetite, backache, headache, andsometimes lymphadenopathy. The fever usually peaksin the evening and slowly returns to normal by morning.The slow rise in temperature during the day, decliningat night, has led to its other name, undulant fever.These symptoms can last from months to years, but for- Figure 11-5tunately the disease is rarely fatal. Diagnosis of active disease is best made by culture ofthe organism from the blood, bone marrow, liver, orlymph nodes. Serologic examination that demonstrates This bacterium causes the most frequent wound in-elevated anti-Brucella antibodies suggests active dis- fection following a cat or dog bite. When a patient comesease. A skin test (with brucellergin) similar to that for in with a cat or dog bite (or scratch), it is important nottularemia is available, but a positive result only indi- to close the wound with sutures. A closed wound createscates exposure to the organism and does not prove that a pleasant environment for Pasteurella multocidathere is active brucellosis. growth, and the resulting infection can invade local joints and bones. Treat infected patients with penicillinPasteurella multocida or doxycycline. This organism is a gram-negative zoonotic organism. Fig. 11-6. Summary of zoonotic gram-negative rods.However, it is NOT a facultative intracellular organ-ism!!!! This bacterium colonizes the mouths of cats Recommended Review Articles:much in the same way that Streptococcus viridans colo-nizes the human nasopharynx. It also causes disease in Gill V, Cunha B. Tularemia Pneumonia; Seminars in Respi-other mammals and birds. ratory Infections, Vol 12, No. 1; 1997; 61-67. Titball R, Leary S. Plague. British Medical Bulletin 1998;54:Fig. 11-5. Cat chasing a bird in a"Pasteur." 625-633. 76
  • 82. M. Gladwin and B. Trattler, Clinical Microbiology Made Ridiculously Simple ©MedMasterFigure 11-6 ZOONOTIC GRAM-NEGATIVE RODS
  • 83. CHAPTER 12. CHLAMYDIA, RICKETTSIA, AND FRIENDSChlamydia and Rickettsia are 2 groups of gram-negative both RNA and DNA (while viruses have either DNA orbacteria that are obligate intracellular parasites. This RNA). Also, unlike viruses they both synthesize theirmeans they can survive only by establishing "residence" own proteins and are sensitive to antibiotics.inside animal cells. They need their hosts ATP as an en-ergy source for their own cellular activity. They are Fig. 12-1. Comparison of Chlamydia and Rickettsiaenergy parasites, using a cell membrane transport with bacteria and viruses.system that steals an ATP from the host cell and spitsout an ADP. Both Chlamydia and Rickettsia have this Chlamydia and Rickettsia cause many distinct hu-ATP/ADP translocator. They differ in that Rickettsia man diseases. Chlamydia spreads by person-to-personcan oxidize certain molecules and create ATP (via ox- contact, while Rickettsia spreads by an arthropod vector.idative phosphorylation) while Chlamydia does not ap- CHLAMYDIApear to have this cytochrome system and in fact has nomechanism for ATP production. The obligate intracellu-lar existence brings up 2 questions: Chlamydia is extremely tiny. It is classified as gram- Q: How do we grow and isolate these creatures when negative because it stains red with Gram stain tech-nonliving media do not contain ATP??? nique and has an inner and outer membrane. Unlike A: Indeed, the obligate intracellular existence makes other gram-negative bacteria, it does not have a pepti-it impossible to culture these organisms on nonliving ar- doglycan layer and has no muramic acid.tificial media. However, we can inoculate Chlamydia orRickettsia into living cells (most commonly chick em- Fig. 12-2. Chlamydia wearing his CLAM necklacebryo yolk sac or cell culture). next to a herpes virus demonstrating that Chlamydia Q: Are these bacteria really viruses, since they is about the same size as some of the large viruses.are very tiny and use the hosts cell for their ownreproduction???? Chlamydia is especially fond of columnar epithelial A: Although Chlamydia and Rickettsia share a few cells that line mucous membranes. This correlates wellcharacteristics with viruses (such as their small size with the types of infection that Chlamydia causes, in-and being obligate intracellular parasites), they have cluding conjunctivitis, cervicitis, and pneumonia. Bacteria Chlamydiae Viruses and rickettsiae Size(nm.) 300-3000 350 15-350 Obligatory No YES YES intracellular parasites Nucleic acids RNA & DNA RNA & DNA RNA Q8 DNA Reproduction Fission Complex Synthesis and cycle with assembly fission Antibiotic YES YES NO sensitivity Ribosomes YES YES NO Metabolic YES YES NO enzymes Energy YES NO NO production Figure 12-1 COMPARISON OF CHLAMYDIA AND RICKETTSIA WITH BACTERIA AND VIRUSES 78
  • 84. CHAPTER 12. CHLAMYDIA, RICKETTSIA, AND FRIENDS ing the initial body (IB). Although the IB synthesizes its own DNA, RNA, and proteins, it requires ATP from the host. Therefore, Chlamydia is considered an energy par- asite as well as an intracellular parasite. Fig. 12-4. The Chlamydia life cycle: A) The infectious particle is the elementary body (EB). The EB attaches to and enters (via endocytosis) colum- nar epithelial cells that line mucous membranes. B) Once within an endosome, the EB inhibits phago- some-lysosome fusion and is not destroyed. It trans- forms into an initial body (IB). C) Once enough IBs have formed, some transform backFigure 12-2 into EB. D) The life cycle is completed when the host cell liber- The Chlamydia life cycle is complex as the bacteria ates the elementary body (EB), which can now infectexist in 2 forms: more cells. 1) Elementary body (EB): This is a metabolicallyinert (does not divide), dense, round, small (300 nm.), in- There are 3 species of Chlamydia. Chlamydia tra- chomatis primarily infect the eyes, genitals, and lungs;fectious particle. The outer membrane has extensivedisulfide bond cross-linkages that confer stability for ex- Chlamydia psittaci and Chlamydia pneumonia onlytracellular existence. infect the lungs. All are treated with tetracycline or erythromycin.Fig. 12-3. Think of the elementary body as an ele-mentary weapon like the cannon ball, fired from host Fig. 12-5. Chlamydial diseases.cell to host cell, spreading the infection. 2) Initial body (also called reticulate body): Once Chlamydia trachomatisinside a host cell the elementary body inhibits phago- Fig. 12-6. Chlamydia trachomatis primarily infectssome-lysosome fusion, and grows in size to 1000 nm. Its the eyes and genitals. Picture a flower child withRNA content increases, and binary fission occurs, form- groovy clam eyeglasses and a clam bikini. Figure 12-3 79
  • 85. CHAPTER 12. CHLAMYDIA, RICKETTSIA, AND FRIENDS Figure 12-4 Species Disease Chlamydia trachomatis serotypes A, B, & C T rachoma (a leading cause of blindness in the world) 1. Inclusion conjunctivitis (usually in newborns, contracted in the birth serotypes D thru K canal) 2. Infant pneumonia 3. Cervicitis 4. Nongonococcal urethritis in men serotypes Lt, L2, L3 Lymphogranuloma venereum (LGV) Chlamydia psittaci Atypical pneumonia Chlamydia pneumoniae .Atypical pneumonia Serogroup TWAR Figure 12-5 CHLAMYDIAL DISEASESTrachoma hand transfer of infected eye secretions and by sharing contaminated clothing or towels. Blindness develops Chlamydia trachomatis is responsible for trachoma, slowly over 10-15 years.a type of chronic conjunctivitis that is currently theleading cause of preventable blindness in the world. Fig. 12-7. The conjunctival infection causes inflam-It is a disease of poverty, prevalent in underdeveloped mation and scarring. Scar traction (trachtion for trach-parts of the world. In the U. S., Native Americans are oma) pulls and folds the eyelid inward so that thethe group most frequently infected. Children act as the eyelashes rub against the conjunctiva and cornea,main reservoir, and transmission occurs by hand-to- which causes corneal scarring, secondary bacterial in- 80
  • 86. CHAPTER 12. CHLAMYDIA, RICKETTSIA, AND FRIENDS Figure 12-6fections, and ultimately blindness. Simple treatmentwith topical tetracycline prevents this illness.Inclusion Conjunctivitis As Chlamydia trachomatis is the most common sexu- ally transmitted disease in the U. S., it is not surprising that many babies delivered through birth canals in-fected with this organism develop inclusion conjunc- Figure 12-7tivitis. Conjunctival inflammation with a purulent antibodies and/or demonstration of Chlamydia tra-yellow discharge and swelling of the eyelids usually chomatis in clinical specimens. Treat with oral ery-arises 5-14 days after birth. In the U. S., all newborns thromycin.are given erythromycin eye drops prophylactically. Diagnosis is made by demonstrating basophilic in- Urethritistracytoplasmic inclusion bodies in cells taken fromscrapings of the palpebral conjunctival surface. These Urethritis, an infection of the urethra, is usually con-inclusion bodies are collections of initial bodies in the cy- tracted sexually. Neisseria gonorrhoeae is the most fa-toplasm of the conjunctival cells. mous bacterium causing urethritis, but not the most common. Urethritis that is not caused by Neisseria gon- orrhoeae is called nongonococcal urethritis (NGU), andInfant Pneumonia is thought to be the most common sexually transmit- A babys passage through an infected birth canal may ted disease. NGU is predominantly caused by Chlamy-also lead to a chlamydial pneumonia, which usually oc- dia trachomatis and Ureaplasma urealyticum.curs between 4-11 weeks of life. Initially, the infant de- Many patients with NGU are asymptomatic. Symp-velops upper respiratory symptoms followed by rapid tomatic patients develop painful urination (dysuria)breathing, cough, and respiratory distress. along with a thin to thick, mucoid discharge from the Diagnosis is made clinically, and the diagnosis can be urethra. It is impossible clinically to differentiate gono-later confirmed by the presence of anti-chlamydial IgM coccal urethritis from NGU and they often occur to- 81
  • 87. CHAPTER 12. CHLAMYDIA, RICKETTSIA, AND FRIENDS gether as a mixed infection. These mixed infections are chronic pelvic pain. It is estimated that 1 million women discovered when patients are treated only with a peni- suffer from PID every year in the U.S. and 25% of them cillin family antibiotic and dont get better. Penicillins will become infertile. In one prospective study (We- treat the gonorrhea, but are ineffective against Chlamy- strom, 1992), tubal occlusion leading to infertility oc- dia trachomatis. Remember that Chlamydia trachoma- curred in 8% of women after 1 episode of PID, 19.5% tis has no peptidoglycan layer, which is the target for after 2 episodes, and 40% after 3 episodes. Likewise, the penicillin. risk of ectopic pregnancy and chronic pelvic pain in- Therefore, all patients diagnosed with urethritis are creases with recurrent PID. empirically treated with antibiotics to cover Neisseria Chlamydia trachomatis is particularly dangerous asgonorrhoeae, Chlamydia trachomatis, and Ureaplasma it often causes asymptomatic or mild PID that goes un- urealyticum. A commonly used treatment regimen in- diagnosed and untreated, yet can still lead to infertility. volves a single dose of intramuscular ceftriaxone (athird-generation cephalosporin that is extremely effec- Fig. 12-8. Infected fallopian tubes scar easily, whichtive against Neisseria gonorrhoeae) followed by a 7-day can result in infertility. The silent sinister CLAMcourse of oral doxycycline or 1 oral dose of azithromycin (Chlamydia trachomatis) causes asymptomatic PID( which covers both Chlamydia trachomatis and Urea- that can lead to infertility.plasma urealyticum). (See Chapter 17, page 131.) While the patient is on empiric antibiotics, diagnostic A simple shot of ceftriaxone and 14 days of oraltests are performed to determine which organism is re- doxycycline will vanquish PID.sponsible. The diagnosis of chlamydial NGU is a bitroundabout because the bacteria are too small to visu- ( McCormack, 1994)alize with the Gram stain and cannot be cultured onnonliving media. If the Gram stain reveals polymor- Epididymitisphonuclear leukocytes but NO intracellular or extracel-lular gram-negative diplococci (that is, NO Neisseria Chlamydial epididymitis can develop in men withgonorrhoeae ), a diagnosis of NGU is likely. If cultures urethritis and presents clinically as unilateral scrotalfail to grow the Neisseria gonorrhoeae, then a diagnosis swelling, tenderness, and pain, associated with fever.of NGU is further supported. The discharge can also besmeared on a slide and sent for a chlamydial comple- Other Complications ofment fixation test for absolute confirmation. Chlamydial Infection Chlamydia trachomatis is also linked to ReitersCervicitis and Pelvic Inflammatory Disease syndrome, an inflammatory arthritis of large joints,(PID) The cervix is a frequent site for Chlamydia tra-chomatis infection. The inflamed cervix appears red, swollen, and has a yellow mucopurulent endocervical discharge. This infection can spread upwards to involvethe uterus, fallopian tubes, and ovaries. This infection,which can be caused by both Chlamydia trachomatis and Neisseria gonorrhoeae, is called pelvic inflamma-tory disease (PID). Women with PID often develop abnormal vaginal dis-charge or uterine bleeding, pain with sexual intercourse(dyspareunia), nausea, vomiting, and fever. The mostcommon symptom is lower abdominal pain. The in-flamed cervix, uterus, tubes, and ovaries are verypainful. Some medical slang emphasizes this. Womenare observed to have the "PID shuffle" (small, wide-based steps to minimize shaking of abdomen). Withmovement of the cervix on bimanual vaginal examina-tion the patient may exhibit the "Chandelier sign" (cer-vical motion tenderness is so severe that the patientleaps to the chandelier). PID often results in fallopian tube scarring, whichcan cause infertility, tubal (ectopic) pregnancy, and Figure 12-8 82
  • 88. CHAPTER 12. CHLAMYDIA, RICKETTSIA, AND FRIENDS that commonly occurs in young men between the ages of 20 and 40. Inflammation of the eyes (uveitis and con- junctivitis) and urethritis also occur. However, other in- fectious agents may also precipitate this syndrome. Fitz-Hugh-Curtis syndrome is an infection of the liver capsule with symptoms of right upper quadrant pain that can occur in men and women. This syndrome is associated with either chlamydial or gonococcal in- fection. Lymphogranuloma Venereum Lymphogranuloma venereum, another sexually transmitted disease caused by Chlamydia trachomatis, (serotypes L1, L2 and L3) starts with a painless papule (bump) or ulceration on the genitals that heals sponta- Figure 12-9 neously. The bacteria migrate to regional lymph nodes, which enlarge over the next 2 months. These nodes be- Chlamydia pneumoniae come increasingly tender and may break open and drain (strain TWAR) pus (see Chapter 10, page 69). Chlamydia pneumonia TWAR is a recently identified species of Chlamydia, which is transmitted from personChlamydia psittaci to person by the respiratory route and causes an atypi-(Psittacosis) cal pneumonia in young adults worldwide (along with Mycoplasma pneumoniae). TWAR is an acronym for its Chlamydia psittaci infects more than 130 species of original isolation in Taiwan and Acute Respiratory.birds, even pet parrots. Humans are infected by inhalingChlamydia-laden dust from feathers or dried-out feces.This infection is an occupational hazard for breeders ofcarrier pigeons, veterinarians, and workers in pet-shops RICKETTSIAor poultry slaughterhouses. Infection results in an atyp- Rickettsia is a small, gram-negative, non-motile, rod-ical pneumonia called psittacosis, which occurs 1-3 to coccoid-shaped bacterium. It is similar to Chlamydiaweeks after exposure. in that they both are the size of large viruses. Both are obligate intracellular energy parasites (they steal ATP). However, Rickettsia differs from Chlamydia in a num-Atypical Pneumonia ber of ways: Pneumonia caused by viruses, Mycoplasma pneumo- 1) Rickettsia requires an arthropod vector (except for niae, Chlamydia psittaci, and Chlamydia pneumoniae, Q fever). are called atypical pneumonias because the pneu-monia is very different from a typical bacterial pneu- Fig. 12-10. Ricky the riding Rickettsia loves tomonia caused by Streptococcus pneumonia. Patients travel. He rides a tick in Rocky Mountain spotted fever,with atypical pneumonia present with fever, headache, a louse in epidemic typhus, and a flea in endemic typhus.and a dry hacking cough without production of yellowsputum. The lung exam is surprisingly normal with 2) Rickettsia replicates freely in the cytoplasm, inonly a few crackles heard with the stethoscope. The contrast to Chlamydia, which replicates in endosomeschest X-ray may have patches or streaks of infiltrate. (inclusions).In contrast, a patient with a streptococcal pneumonia 3) Rickettsia has a tropism for endothelial cells thatappears very sick, coughs up gobs of pus, and has a line blood vessels ( Chlamydia likes columnar epithe-lobe of the lung socked in with white blood cells and lium).debris that can be heard on physical exam and seen on 4) They cause different diseases!!! Most Rickettsiachest X-ray. cause rashes, high fevers, and bad headaches.Fig. 12-9. A man with atypical pneumonia caused by Some Rickettsia share antigenic characteristics withChlamydia psittaci. He has a bird with a CLAM neck- certain strains of Proteus vulgaris bacteria. It is purelylace, PSITTING on his shoulder. coincidental that they have the same antigens. Proteus 83
  • 89. CHAPTER 12. CHLAMYDIA, RICKETTSIA, AND FRIENDSFigure 12-10is not involved at all in rickettsial disease. The Proteus Fig. 12-11. Antigenic differences among thevulgaris strains that share these common antigens are Rickettsiae.designated OX-2, OX-19, and OX-K. Diagnosis of a rickettsial infection can also be made The Weil-Felix reaction is a classic test that uses with specific serologic tests documenting a rise in anti-these cross-reacting Proteus vulgaris antigens to help Rickettsial antibody titers over time. These include theconfirm a diagnosis of a rickettsial infection. This test indirect immunofluorescence test (IFA), the comple-is done by mixing the serum of a patient suspected of ment fixation test (CF), and the enzyme-linked immu-having a rickettsial disease, with antigens from speci- nosorbent assay (ELISA). These tests can specificallyfic strains of Proteus vulgaris. If the serum has anti- identify species and even subspecies.rickettsial antibodies, latex beads coated with Proteus Therapy for all rickettsial diseases consists primarilyantigens will agglutinate, indicating a positive Weil- of doxycycline and chloramphenicol.Felix test. Comparison of the laboratory results withFig. 12-11 can even help distinguish specific rickettsialdiseases. For example, when this test is performed on a Rickettsia rickettsiapatient with signs and symptoms of a scrub typhus in- (Rocky Mountain Spotted Fever)fection, a negative OX-19 and OX-2 along with a posi-tive OX-K is confirmatory. Ricky is riding a wood tick 84
  • 90. CHAPTER 12. CHLAMYDIA, RICKETTSIA, AND FRIENDS Disease Weil-Felix OX-19 Ox-2 OX-K Rocky Mountain + + - spotted fever Rickettsial pox - - - Epidemic typhus + - - Endemic typhus + - - Brill-Zinsser disease +1- - - Scrub typhus - - + Trench fever - - - - - - Figure 12-11 WEIL-FELIX Fig. 12-12. Rocky Mountain spotted fever presents organism, Rickettsia rickettsia. This disease is char- within a week after a person is bitten by either the wood acterized by fever, conjunctival redness, severe head- tick Dermacentor andersoni or the dog tick Dermacentor ache, and a rash that initially appears on the wrists,variabilis. Both of these ticks transmit the causative ankles, soles and palms and later spreads to the trunk.Figure 12-12 85
  • 91. CHAPTER 12. CHLAMYDIA, RICKETTSIA, AND FRIENDSThis figure illustrates the spotted Rocky Mountains there is a dramatic response to doxycycline. Elimina-behind a boy with headache, fever, palmar rash, and tion of nearby rodents, which can serve as a reservoir fortick infestation. Rickettsia akari, is i mportant in preventing this disease. Rocky Mountain spotted fever is more common in the Rickettsia prowazekiisoutheastern U. S. tick belt than in the Rocky Mountainregion. This disease should be called Appalachian spot- (Epidemic Typhus)ted fever, as most cases currently occur in the south At- Ricky is riding a louse... .lantic and south central states such as North Carolina, An epidemic is the sudden onset and rapid spread ofSouth Carolina, Tennessee, and Oklahoma. However, an infection that affects a large proportion of a popula-cases have been reported in nearly every state. tion. Endemic refers to an infectious disease that ex- The organisms proliferate in the endothelial lining of ists constantly throughout a population. Two species ofsmall blood vessels and capillaries, causing small hem- Rickettsia cause typhus. Rickettsia prowazekii causesorrhages and thrombi. The inflammation and damage to an epidemic form, while Rickettsia typhi is responsiblesmall blood vessels explains the conjunctival redness for endemic typhus. Although they have different reser-and skin rash. Although this disease often resolves in voirs and vectors, these are closely related bacteria thatabout 3 weeks, it can progress to death (especially when cause a similar disease, and infection with one confersantibiotic therapy is delayed). immunity to the other!! Since the tick transmits this bacteria during its 6-10hours of feeding, early discovery and removal of tickswill prevent infection (Spach, 1993). Fig. 12.14. Prowazekia is Prower!!! With war, over- crowding, and poverty, unsanitary conditions prevail and lice take control, harboring Rickettsia prowazekii.Rickettsia akari The lice transmit the bacteria to humans, causing epi-(Rickettsialpox) demic typhus.Ricky is riding a mite.... This disease wiped out a third of Napoleons armyFig. 12-13. Rickettsia akari causes rickettsialpox when he advanced on Moscow in 1812, and was respon-and is transmitted to humans via mites that live on sible for more than 3 million Russian deaths in Worldhouse mice. Imagine Ricky, with pox marks, playing War I. The last epidemic in the U. S. occurred more thanAtari (old type of Nintendo) with his rodent friend 70 years ago. Currently, flying squirrels serve as amatey mouse. reservoir in the southern U. S. Sporadic cases occur Rickettsialpox is a mild, self-limited, febrile disease when lice or fleas from infected squirrels bite humans.that starts with an initial localized red skin bump Clinically, epidemic typhus is characterized by an(papule) at the site of the mite bite. The bump turns into abrupt onset of fever and headache following a 2-weeka blister (vescicle) and days later fever and headache de- incubation period. Small pink macules appear aroundvelop, and other vescicles appear over the body (similar the fifth day on the upper trunk and quickly cover theto chickenpox). Although this disease is self-limiting, entire body. In contrast to Rocky Mountain spotted fever, this rash spares the palms, soles, and face. The patient may become delirious or stuporous. Since Rick- ettsia invade the endothelial cells of blood vessels, there is an increased risk of blood vessel clotting leading to gangrene of the feet or hands. This disease will often re- solve by 3 weeks, but occasionally is fatal (especially in older patients). Diagnosis would be easy during an epidemic. The poor doctor with Napoleons retreating forces surely be- came an expert diagnostician of louse-borne typhus! It is the sporadic case in the southern U.S., transmitted from flying squirrels to humans by louse or flea bites, that is unexpected and thus difficult to diagnose. Close contact with the flying squirrel vector should raise sus- picion. Besides tetracycline and chloramphenicol, improved sanitation and eradication of human lice will help con-Figure 12-13 trol epidemics. 86
  • 92. CHAPTER 12. CHLAMYDIA, RICKETTSIA, AND FRIENDS Figure 12-14Brill-Zinsser Disease cheopis. (This flea was also responsible for transmission of bubonic plague in the past.) For those of you who have referred to the Zinsser Mi- Following a 10-day incubation period, fever, head- crobiology textbook, it is interesting to note that Hans ache, and a flat and sometimes bumpy (maculopapular) Zinsser is credited with correctly postulating that pa- rash develop, just as with epidemic typhus. Although tients who recovered without antibiotic therapy from this disease is milder than that caused by epidemic ty- epidemic louse-borne typhus could still retain the phus, it is still very serious. pathogen Rickettsia prowazekii in a latent state. Occa- Treat with doxycycline or chloramphenicol. Controlsionally, it breaks out of its latent state to produce Brill- flea and rat populations. As with the bubonic plagueZinsser disease. However, symptoms are usually milder (Yersinia pestis), we dont want to just kill the rats because(no skin rash) due to the presence of pre-formed anti- the starving fleas would then all move to bite humans!!!bodies from the original infection. Diagnosis is made bydemonstrating a rapid early rise in IgG titer specific for Rickettsia tsutsugamushiRickettsia prowazekii, rather than a rapid rise in IgM,which occurs in the primary infection. (Scrub Typhus, or Tsutsugamushi Fever) It is always important to completely eradicate Rick- Rickettsia tsutsugamushi is found in Asia and theettsia prowazekii from your patient with sufficient an- southwest Pacific. This disease affected soldiers in thetibiotic therapy because untreated patients may serve South Pacific during World War II and in a reservoir between epidemics. Rickettsia tsutsugamushi is spread by the bite of larvae (chiggers) of mites. The mites live on rodents, and theRickettsia typhi larval chiggers live in the soil.(Endemic or Murine Typhus) Fig. 12-15. Ricky is now a South Pacific sumoRicky is riding a flea... . wrestler named Ricky Tsutsugamushi. He is walking in Endemic flea-borne typhus is similar to epidemic the scrub (scrub typhus) being bitten by chiggers thattyphus, yet it is not as severe and does not occur in are on his feet and legs.epidemics. This disease is caused by Rickettsia typhi.Rodents serve as the primary reservoir, and the disease After a 2-week incubation period, there is high fever,is transmitted to humans via the rat flea, Xenopsylla headache, and a scab at the original bite site. Later 87
  • 93. CHAPTER 12. CHLAMYDIA, RICKETTSIA, AND FRIENDS ever, there is now growing evidence that another bac- terium may be the etiologic agent: Bartonella henselae. Several studies have now documented high levels of anti-Bartonella henselae antibodies in patients with cat-scratch disease. Bartonella henselae may also be re- sponsible for a disease called bacillary angiomatosis, which involves a proliferation of small blood vessels in the skin and organs of AIDS patients (Margileth, 1993; Zangwill, 1993). Coxiella burnetii ( Q Fever) Coxiella burnetii is unique to the Rickettsia because, like the gram-positive spore formers (Clostridium andFigure 12-15 Bacillus), it has an endospore form. This endospore confers properties to the bacteria that differ from othera flat and sometimes bumpy (maculopapular) rash Rickettsiae:develops. 1) Resistance to heat and drying: Spores mayBartonella (formerly Rochalimaea contaminate milk products so pasteurization tempera- tures have to be raised to greater than 60°C to kill thequintana) endospores.( Trench Fever) 2) Extracellular existence: The spores resistance Trench fever is a louse-borne febrile disease that oc- allows extended survival outside a host cell. However,curred during World War I. The organism responsible like Chlamydia and Rickettsia, growth and divisionfor this disease is Bartonella quintana. Although it is must occur intracellularly using the hosts ATP.Rickettsia-like, it has a different genus name because it 3) Non-arthropod transmission: Coxiella burnetiiis not an obligate intracellular organism. grows in ticks and cattle. The spores remain viable in This disease was spread in the trenches by the body dried tick feces deposited on cattle hides, and in driedlouse. Infected soldiers developed high fevers, rash, cow placentas following birthing. These spores areheadache, and severe back and leg pains. After appear- aerosolized and when inhaled cause human to recover, the soldier would relapse 5 days later. Spore inhalation rather than an arthropod bite causesMultiple relapses can occur but fatalities are rare. The Q fever.organisms species name, quintana, reflects the charac- 4) Pneumonia: Because the spores are inhaled intoteristic 5-day interval between febrile episodes. the lungs, a mild pneumonia similar to that of a My- Notice the similarities here with epidemic typhus coplasma pneumonia often develops.( Rickettsia prowazekii-Prowar Ricky). Both achieve epi-demic proportions during war, when filth and poor san- Clinically, abrupt onset of fever and soaking sweatsitation lead to lice overgrowth. occur 2-3 weeks after infection, along with a pneumo- nia. This is the only rickettsial disease that causes FILTH = LICE _ pneumonia and in which there is NO rash. Rickettsia prowazekii (Epidemic typhus) + Bartonella quintana (trench fever) Fig. 12-16. Visualize Carol Burnett (Coxiella bur- netti) coughing after inhaling the spores from a cowhideBartonella (formerly Rochalimaea) and dried placental products in the grass.henselae( Cat-scratch Disease and Bacillary Angiomatosis) Ehrlichia canis and chaffeensis ( Ehrlichiosis and Human Ehrlichiosis) Cat-scratch disease occurs following a cat bite orscratch. A regional lymph node or nodes will enlarge Ehrlichia canis is a disease of dogs. This makes senseand the patient may develop low-grade fever and since dogs like to LICK. Dogs get the bacteria from ticksmalaise. The disease usually resolves within a few which jump from dog to dog. The ticks can also bite hu-months without complications. mans, transmitting a very close relative of Ehrlichia ca- A motile, gram-negative rod named Afipia fells nis to humans. This bacterium is now called Ehrlichiawas originally isolated from affected lymph nodes. How- chaffeensis and causes a disease (called human ehrli- 88
  • 94. CHAPTER 12. CHLAMYDIA, RICKETTSIA, AND FRIENDS chiosis) very similar to Rocky Mountain spotted fever. Patients develop high fever and severe headache, but rarely (only 20% of the time) rash (Spach, 1993). Fig. 12-17. Summary chart of Chlamydia and Rickettsia. References Margileth AM, Hayden GF. Cat Scratch Disease From Feline Affection to Human Infection. N Engl J Med 1993; 329:53-54. McCormack WM. Current Concepts: Pelvic Inflammatory Dis- ease. N Engl J Med 1994;330:115-119. Spach DH, et al. Tick-borne diseases in the United States. N Engl J Med 1993;329:936-947. Westrom L, et. al. Pelvic inflammatory disease and fertility: a cohort study of 1,844 women with laparoscopically verifiedFigure 12-16 disease and 657 control women with normal laparoscopic results. Sex Transm Dis 1992;19:185-92. Zangwill KM, et al. Cat Scratch Disease in Connecticut: Epi- demiology, Risk Factors, and Evaluation of a New Diag- nostic Test. N Engl J Med 1993;329:8-13. 89
  • 95. Figure 12-17 GRAM-NEGATIVE OBLIGATE INTRACELLULAR PARASITES: CHLAMYDIA AND RICKETTSIAGla dwin a nd B T rattle r Clinical Microbiology Made Ridiculously Simple
  • 96. CHAPTER 13. SPIROCHETES Spirochetes are tiny gram-negative organisms that look P ainless chancre (ulcer) Stage Clinical like corkscrews. They move in a unique spinning mo- Primary stage ion via 6 thin endoflagella called axial filaments, Secondary stage 1. Rash on palms and soles which lie between the outer membrane and peptidogly- 2. Condyloma latum can layer and wrap around the length of the spirochete. 3. CNS, eyes, bones, kidneys 2 5% may relapse and develop These organisms replicate by transverse fission. and/or joints can be involved Spirochetes are a diagnostic problem. They cannot Latent syphilis be cultured in ordinary media, and although they have secondary stage symptoms again gram-negative cell membranes, they are too small to Tertiary stage 1. Gummas of skin and bone be seen using the light microscope. Special proce- 2. Cardiovascular (aortic aneurysm) dures are required to view these organisms, including 3. Neurosyphilis darkfield microscopy, immunofluorescence, and silver Figure 13-1 SYPHILIS: CLINICAL stains. Also, serologic tests help screen for infections with spirochetes. MANIFESTATIONS Spirochetes are divided into 3 genera: 1) Treponema, Fig. 13-2. The chancre can be described as a firm, ul- 2) Borrelia, and 3) Leptospira. cerated painless lesion with a punched-out base and rolled edges. It is highly infectious, since Treponema TREPONEMA pallidum sheds from it continuously. Think of this skin ulcer as a small Treponema pallidum resort swimming Treponemes produce no known toxins or tissue de- pool, with thousands of vacationers swimming within. structive enzymes. Instead, many of the disease mani- The chancre resolves over 4-6 weeks without a scar, of- festations are caused by the hosts own immune ten fooling the infected individual into thinking that the responses, such as inflammatory cell infiltrates, prolif- infection has completely resolved. erative vascular changes, and granuloma formation. Treponema pallidum ( Syphilis) Treponema pallidum is the infectious agent responsi- ble for the sexually transmitted disease syphilis. The number of new cases of syphilis has been increasing since 1956, with more than 100 thousand cases reported in 1990 in the U.S. Black heterosexual men and women living in urban centers are at highest risk for acquiring Figure 13-2 syphilis today. Treponema pallidum enters the body by penetrating Secondary Syphilis intact mucous membranes or by invading through ep- ithelial abrasions. Skin contact with an ulcer infected Untreated patients enter the bacteremic stage, or sec-with Treponema pallidum (even by the doctors exam- ondary syphilis, often about 6 weeks after the primary chancre has healed (although sometimes the manifesta-ining hand) can result in infection. When infection oc-curs, the spirochetes immediately begin disseminating tions of secondary syphilis occur while the primary chan-throughout the body. cre is still healing). In secondary syphilis, the bacteria If untreated, patients with syphilis will progress multiply and spread via the blood throughout the body.through 3 clinical stages, with a latent period between Unlike the single lesion of primary syphilis, the secondstages 2 and 3. stage is systemic, with widespread rash, generalized lymphadenopathy, and involvement of many organs.Fig. 13-1. Stages of syphilis. The rash of secondary syphilis consists of small red macular (flat) lesions symmetrically distributed over the body, particularly involving the palms, soles, andPrimary Syphilis mucous membranes of the oral cavity. The skin lesions The primary lesion of syphilis is a painless chancre can become papular (bumpy) and even pustular.that erupts at the site of inoculation 3-6 weeks after the A second characteristic skin finding of the secondinitial contact. Regional nontender lymph node swelling stage is called condyloma latum. This painless, wart-occurs as well. like lesion often occurs in warm, moist sites like the 91
  • 97. CHAPTER 13. SPIROCHETESvulva or scrotum. This lesion, which is packed with spiro-chetes, ulcerates and is therefore extremely contagious. Skin infection in areas of hair growth results inpatchy bald spots and loss of eyebrows. During the secondary stage, almost any organ can be-come infected (including the CNS, eyes, kidneys, andbones). Systemic symptoms, such as generalized lym-phadenopathy, weight loss, and fever, also occur duringthis stage. The rash and condyloma lata resolve over 6 weeks,and this disease enters the latent phase.Latent Syphilis In this stage, the features of secondary syphilis haveresolved, although serologic tests remain positive. Mostpatients are asymptomatic during this period, althoughabout 25% will have one or more relapses and developthe infectious skin lesions of secondary syphilis. After 4 Figure 13-3years, there are generally no more relapses, and this dis-ease is now considered noninfectious (except in pregnant 3) Neurosyphilis occurs in about 8% of untreatedwomen, who can still transmit syphilis to their fetus). cases. The 5 most common presentations of neurosyphi- About one-third of untreated patients will slowly lis are:progress from this stage to tertiary syphilis. The rest a) Asymptomatic neurosyphilis: The patientwill remain asymptomatic. is clinically normal, but cerebrospinal fluid tests positive for syphilis.Tertiary Syphilis b) Subacute meningitis: The patient has fever, stiff neck, and headache. Cerebrospinal fluid analy- Tertiary syphilis generally develops over 6-40 years, sis reveals a high lymphocyte count, high protein,with slow inflammatory damage to organ tissue, small low glucose, and positive syphilis tests.blood vessels, and nerve cells. It can be grouped into 3 Note that most bacteria cause an acute meningitisgeneral categories: 1) gummatous syphilis, 2) cardio- with a high neutrophil count, high protein, and lowvascular syphilis, and 3) neurosyphilis. glucose. Treponema pallidum and Mycobacterium 1) Gummatous syphilis occurs 3-10 years after the tuberculosis are two bacteria that cause a subacuteprimary infection in 15%n of untreated patients. meningitis with a predominance of lymphocytes. c) Meningovascular syphilis: The spirochetesFig. 13-3. Gummas (Gummy bears) are localized attack blood vessels in the brain and meninges (cir-granulomatous lesions which eventually necrose and cle of Willis!), resulting in cerebrovascular occlusionbecome fibrotic. These noninfectious lesions are found and infarction of the nerve tissue in the brain,mainly in the skin and bones. Skin gummas are pain- spinal cord, and meninges, causing a spectrum ofless solitary lesions with sharp borders, while bone le- neurologic impairments.sions are associated with a deep gnawing pain. These d) Tabes dorsalis: This condition affects thewill resolve with antimicrobial therapy. spinal cord, specifically the posterior column and dorsal roots. 2) Cardiovascular syphilis occurs at least 10years after the primary infection in 10% of untreated Fig. 13-4. Syphilitic tabes dorsalis involves damage patients. Characteristically, an aneurysm forms in the to the posterior columns and dorsal roots of the spinalascending aorta or aortic arch. This is caused by chronic cord. Posterior column damage disrupts vibratory andinflammatory destruction of the small arterioles (vasa proprioceptive sensations, resulting in ataxia. Dorsalvasorum) supplying the aorta itself, leading to necrosis root and ganglia damage leads to loss of reflexes andof the media layer of the aorta. The wall of the aorta loss of pain and temperature sensation.splits as blood dissects through the weakened medialayer. Aortic valve insufficiency and occlusion of the e) General paresis (of the insane): This is a pro-coronary arteries may also develop as the dissection gressive disease of the nerve cells in the brain, lead-spreads to involve the coronary arteries. Antimicrobial ing to mental deterioration and psychiatrictherapy can NOT reverse these manifestations. symptoms. 92
  • 98. CHAPTER 13. SPIROCHETES 2) Bone and teeth are frequently involved. Periosteal (outer layer of bone) inflammation destroys the carti- lage of the palate and nasal septum, giving the nose a sunken appearance called saddle nose. A similar in- flammation of the tibia leads to bowing called saber shins. The upper central incisors are widely spaced with a central notch in each tooth ( Hutchinsons teeth) and the molars have too many cusps ( mulberry molars). 3) Eye disease such as corneal inflammation can occur. Figure 13-4 Interestingly, Treponema pallidum infection does not The Argyll-Robertson pupil may be present in damage the fetus until the fourth month of gestation, so both tabes dorsalis and general paresis. The Argyll- treating the mother with antibiotic therapy prior to this Robertson pupil, caused by a midbrain lesion, constricts time can prevent congenital syphilis. during accommodation (near vision) but does not react to light. This is also referred to as the "prostitutes Diagnostic Tests for Syphilis pupil" because the prostitute accommodates but does not react, and is frequently infected with syphilis. Absolute diagnosis during the first and second stages can be made by direct examination, under darkfield mi- Fig. 13-5. Overview of primary, secondary, latent, croscopy, of a specimen from the primary chancre, the and tertiary syphilis. Notice the rule of sixes: maculopapular rash, or the condyloma latum. Darkfield Six-Sexual transmission microscopy reveals tiny helically-shaped organisms 6 axial filaments moving in a corkscrew-like fashion. 6 week incubation Since direct visualization of spirochetes is effective 6 weeks for the ulcer to heal only during the active stages of primary and secondary 6 weeks after the ulcer heals, secondary syphilis syphilis, serologic tests were developed as a screening develops tool. There are 2 types of serologic screening test: non- 6 weeks for secondary syphilis to resolve specific and specific. 66% of latent stage patients have resolution (no ter- tiary syphilis) 1) Nonspecific treponemal tests: Infection with 6 years to develop tertiary syphilis (at the least) syphilis results in cellular damage and the release into the serum of a number of lipids, including cardiolipin Congenital Syphilis and lecithin. The body produces antibodies against these antigens. We therefore quantitatively measure Congenital syphilis occurs in the fetus of an infected the titer of the antibodies that bind to these lipids. If a pregnant woman. Treponema pallidum crosses the pla- patients serum has these antibodies, we suspect that cental blood barrier, and the treponemes rapidly dis- he/she has syphilis. Since invasion of the cerebrospinal seminate throughout the infected fetus. Fetuses that fluid (CSF) by syphilis also stimulates an increase of acquire the infection have a high mortality rate (still- these anti-lipoidal antibodies, we can also perform this birth, spontaneous abortion, and neonatal death), and test on the CSF to diagnose neurosyphilis. The two most almost all of those that survive will develop early or late common tests employing this technique are the Vene- congenital syphilis. real Disease Research Laboratory (VDRL) and Early congenital syphilis occurs within 2 years Rapid Plasma Reagin (RPR) test. and is like severe adult secondary syphilis with wide- So why are these tests nonspecific? It is important tospread rash and condyloma latum. Involvement of the realize that 1% of adults without syphilis will also havenasal mucous membranes leads to a runny nose called these antibodies, resulting in a false positive test. Forthe "snuffles." Lymph node, liver, and spleen enlarge- example, false positive tests often occur in patients whoment, and bone infection (osteitis-seen on X-ray), are are pregnant, have an acute febrile illness such as in-also common afflictions of early congenital syphilis. fectious mononucleosis or viral hepatitis, use intra- venous drugs, or following immunization. Therefore, a Late congenital syphilis is similar to adult tertiarysyphilis except that cardiovascular involvement rarely positive nonspecific test must be confirmed with a spe- cific treponemal antibody test.occurs: 2) Specific treponemal tests: While the nonspe- 1) Neurosyphilis is the same as adults and eighth cific tests look for anti-lipoidal antibodies, the specificnerve deafness is common. treponemal tests look for antibodies against the spiro- 93
  • 100. CHAPTER 13. SPIROCHETES chete itself. TheIndirect Immunofluorescent Tre- VDRL or RPR FTA-ABS I nterpretation ponemal Antibody-Absorption (FTA-ABS) test is + + I ndicates an active the most commonly used specific treponemal test. This treponemal infection test is performed by first mixing the patients serum + - P robably a false positive - + • Successfully treated with a standardized nonpathogenic strain of Tre- syphilis ponema, which removes (absorbs) antibodies shared by - - Syphilis unlikely, although: both Treponema pallidum and the nonpathogenic tre- 1. Patients with a syphilis ponemal strains (as nonpathogenic strains of Tre- i nfection who also have AIDS ponema are part of the normal human flora). The may be sero-negative remaining serum is then added to a slide covered with 2. Patient recently infected killed Treponema pallidum (as the antigen). Antibodies with syphilis may not have that are specific to this organism will subsequently developed an immune bind, giving a positive result. response yet Since we all have antibodies to nonpathogenic strains Note: VDRL and RPR are very similar tests. of treponemes, the absorption part of the FTA-ABS test is necessary to cut down on the number of false posi- tives. Only people who have antibodies specific for the Figure 13-6 SYPHILIS SEROLOGY INTER- pathogenic strain of treponemes will elicit a positive re- PRETATION action. However, false positives can occur with other spirochetal infections, such as yaws, pinta, leptospiro- otics are started. Symptoms include a mild fever, chills, sis, and Lyme disease. malaise, headache, and muscle aches. The killed organ- Treatment isms release a pyrogen (fever-producing enzyme) that is thought to cause these symptoms. This self-limiting re- Treponema pallidum is extremely fragile, and can be action, called the Jarisch-Herxheimer phenome- killed easily with heat, drying, or soap and water. Since non, may occur with most spirochetes. syphilis was found to be treatable by raising ones body temperature, patients in the early 1900s were placed in Treponema pallidum Subspecies a "fever" box (a closed box in the hot sun, with only the patients head protruding). Fortunately, the discovery There are 3 subspecies of Treponema pallidum (en- of penicillin provided a less hazardous therapy. demicum, pertenue, and carateum) that cause non- The current drug of choice for syphilis is penicillin (the venereal disease (endemic syphilis, yaws, and pinta, particular type and dosage of penicillin depends on the respectively). All 3 subspecies cause skin ulcers and stage of the infection). Penicillin can even cross the pla- gummas of the skin and bones in children, with the ex- centa and cure congenital syphilis. Patients allergic to ception of Treponema carateum, which only causes skin penicillin can be effectively treated with erythromycin discoloration (no gummas).and doxycycline (but doxycycline cannot be used to treat Interestingly, these subspecies are morphologicallycongenital syphilis, as it is toxic to the fetus). and genetically identical to Treponema pallidum, yet do It is important to realize that reinfection can occur. not cause the sexually transmitted disease syphilis.This suggests that antitreponemal antibodies are not However, the diseases do share many characteristicsprotective. Cell-mediated immunity may play a role in with syphilis. Like syphilis, the general pattern of thesethe course of syphilis by inducing the regression of the diseases involves a primary skin papule or ulcer devel-lesions of primary and secondary syphilis. oping at the site of inoculation (usually not the genitals). With adequate treatment, the levels of anticardi- This is followed by a secondary stage of widespread skinolipin antibodies will decrease, while the levels of spe- lesions. The tertiary stage is manifested years later bycific antitreponemal antibodies will remain unchanged. gummas of the skin and bones. Unlike tertiary syphilis,Therefore, a person who is adequately treated will even- the tertiary stages of the nonvenereal treponemes dotually manifest (over months to years) a drop in the not involve the heart or central nervous system.VDRL or RPR to nonpositive, while the FTA-ABS will The antibodies produced by these infections will giveremain positive. a positive VDRL and FTA-ABS. One intramuscular in- jection of long-acting penicillin is curative. Treponema pallidum Subspecies endemicumFig. 13-6. Interpretation of syphilis serology.Jarisch-Herxheimer Phenomenon ( Endemic Syphilis: Bejel) Most patients with syphilis will develop an acute Endemic syphilis occurs in the desert zones of Africaworsening of their symptoms immediately after antibi- and the Middle East and is spread by sharing drinking 95
  • 101. CHAPTER 13. SPIROCHETESand eating utensils. Skin lesions usually occur in theoral mucosa and are similar to condyloma lata of sec-ondary syphilis. Gummas of the skin and bone may de=velop later.Treponema pallidum Subspecies pertenue(Yaws) Yaws, a disease of the moist tropics, spreads from per-son to person by contact with open ulcers. At the initialsite of inoculation a papule appears that grows overmonths, becoming wartlike and is called the "motheryaw." Secondary lesions appear on exposed parts of thebody and years later tertiary gummas develop in theskin and long bones.Fig. 13-7. The tertiary lesions in yaws often cause sig-nificant disfigurement of the face. Imagine JAWS(Yaws) taking a bite out of a persons face.Treponema pallidum Subspecies carateum(Pinta)Fig. 13-8. Hispanic person with colored red and blueskin lesions, saying, "Por favor, no pinta mi cabeza."Pinta is purely a skin disease limited to rural LatinAmerica. After infection by direct contact, a papule de-velops which slowly expands. This is followed by a sec-ondary eruption of numerous red lesions that turn bluein the sun. Within a year the lesions become depig-mented, turning white. These colored lesions look likesomeone PAINTED them on. Figure 13-8 BORRELIA The corkscrew-shaped Borrelia are larger than the Borrelia cause Lyme disease (Borrelia burgdorferi)Treponema, and therefore can be viewed under a light and relapsing fever (caused by 18 other species of Bormicroscope with Giemsa or Wright stains. relia). Both of these diseases are transmitted by insect vectors. Borrelia burgdorferi (Lyme Disease) Lyme disease is seen in the Northeast, Midwest and northwestern U. S. This is the most commonly reported tick-borne illness in the U. S. When walking in the woods during the summer months, you must be careful of the Ixodes tick. This tiny creatures bite can transfer the agent for Lyme disease, Borrelia burgdorferi. It takes greater than 24 hours of attachment for transfer of the organism, so regular "tick checks" may help prevent infection. cludes the white-footed mouse (as well as other small ro • The animal reservoir for Borrelia burgdorferi in- up the spirochete from these reservoirs and can subse - dents) and the white-tailed deer. The Ixodes ticks pickFigure 13-7 quently transmit them to humans. 96
  • 102. CHAPTER 13. SPIROCHETES Stage Clinical Early localized stage E rythema chronicum migrans (ECM) (Stage 1) Early disseminated stage 1. Multiple smaller ECM (stage 2) 2. Neurologic: aseptic meningitis, cranial nerve palsies (Bells palsy), and peripheral neuropathy 3. Cardiac: transient heart block or myocarditis 4. Brief attacks of arthritis of large j oints (knee) Late stage 1. Chronic arthritis (stage 3) 2. Encephalopathy Figure 13-9 LYME DISEASE: CLINICAL MANI- FESTATIONS Lyme disease has many features that resemble organ systems: the skin, nervous system, heart, andsyphilis, although Lyme disease is NOT sexually trans- joints. Notice that the Lyme juice (drawn as drops ofmitted. Both of these diseases are caused by spiro- spirochetes) has begun dripping onto the skin, nervouschetes. The primary stage in both involves a single, system, heart, and joints. This stage can occur after orpainless skin lesion (syphilitic chancre and Lymes ery- at the same time as the first stage.thema chronicum migrans) that develops at the initial The skin lesions in this stage are just ECM again,site of inoculation. In both diseases the spirochetes then but this time there are multiple lesions on the body,spread throughout the body, invading many organ sys- and they are smaller (theres just not enough Lymetems, especially the skin. Both also cause chronic prob- juice to make them as large as the one in the primarylems years later (tertiary syphilis and late stage Lyme stage).disease). Borrelia burgdorferi can invade the brain, cranial nerves, and even motor/sensory nerves. Examples in-Fig. 13-9. Like syphilis, Lyme disease has been di- clude meningitis, cranial nerve palsies (especially ofvided into three stages: 1) early localized stage, 2) early the seventh nerve-a Bells palsy), and peripheraldisseminated stage, and 3) late stage. neuropathies.Early Localized Stage The first stage begins about 10 days after the tickbite and lasts about 4 weeks. It consists of just a skinlesion at the site of the tick bite (called erythemachronicum migrans) along with a flulike illness, andregional lymphadenopathy.Fig. 13-10. Erythema chronicum migrans (ECM)starts off as a red (erythematous) flat round rash,which spreads out (or migrates) over time (chron-icum). The outer border remains bright red, while thecenter will clear, turn blue, or even necrose. Visualize adrop of Lyme juice (drawn as drops of spirochetes) land-ing on the skin and the Lyme acid burning the skin red.With time, the juice spreads out and the erythematouslesion spreads, eventually getting so large that there isnot enough juice for the center, so that the center nowhas normal-looking skin.Early Disseminated StageFig. 13-11. The early disseminated stage involves thedissemination of Borrelia burgdorferi spirochetes to 4 Figure 13-10 97
  • 103. CHAPTER 13. SPIROCHETES Figure 13-11 Transient cardiac abnormalities occur in about 10% of in a person who has been exposed to ticks in an area en- If the patient presents with ECM, the leading edge ofpatients. The most common abnormality is atrioventric- demic for Lyme disease. the rash can be biopsied and cultured for Borreliaular nodal block (heart block), and less commonly my-ocarditis and left ventricular dysfunction. Since thecardiac lesions usually resolve in a matter of weeks (es- burgdorferi.pecially with antibiotic therapy), a permanent pace- As culturing this organism from blood and CSF ismaker is often unnecessary. very difficult, determination of the levels of anti-Borre- Migratory joint and muscle pain can also occur. About lia burgdorferi antibodies is often helpful in making a6 months after infection attacks of arthritis can occur. Large diagnosis. The two most effective techniques are en-joints such as the knee become hot, swollen, and painful. zyme-linked immunosorbent assays (ELISA) and West- ern immunoblotting.Late Stage Doxycycline or penicillin family antibiotics are currently the most effective antibiotics for treating this About 10% of untreated patients will develop chronic disease. (Spach, 1993)arthritis that lasts for more than a year. This usually in- Two vaccines have recently been developed for Lymevolves 1 or 2 of the large peripheral joints, such as the disease. Both act by passing antibodies through theknee. Interestingly, many of these patients have the B- individuals blood into the biting tick. The antibodiescell allo-antigen HLA-DR (1 + 4). neutralize bacteria in the tick before they can be trans- Like tertiary syphilis, Lyme disease can lead to mitted to the human. The vaccines are ImuLyme andchronic neurologic damage. An encephalopathy can de- LYMErix.velop characterized by memory impairment, irritability,and somnolence. Borrelia recurrentisDiagnosis and Treatment (Relapsing Fever) Diagnosis primarily depends on the doctors recogniz- Of 18 different species of Borrelia that can cause re-i ng the characteristic clinical findings described above lapsing fever, only Borrelia recurrentis is transmitted to 98
  • 104. CHAPTER 13. SPIROCHETES humans via the body louse ( Pediculus humanus). The other Borrelia species are transmitted by the tick Or- nithodoros. This tick likes to feed on sleeping campers in the western U.S., especially those who sleep in rodent- infested, rustic mountain cabins. After the Borrelia has been transmitted, via the louse or tick, this bacteria disseminates via the blood. A high fever develops, with chills, headaches and muscle aches. Rash and meningeal involvement may follow. With drenching sweats, the fever and symptoms resolve after 3-6 days. The patient remains afebrile for about S days, but then relapses, developing similar features for an- other 3-6 days. Relapses will continue to occur, al- though they will become progressively shorter and milder as the afebrile intervals lengthen.Antigenic Variation: the Key toRelapsing Fever Fig. 13-12. "Why the relapses?" you ask. Well, check out our friend, Boris the Borrelia, who is a master at the art of "antigenic variation." He is initially well cam- ouflaged in blood, but antibodies are soon manufac- tured by the hosts immune system. These antibodies can bind specifically to the Borrelia surface proteins and thereby remove the Borrelia from the blood. But sneaky Boris rapidly changes his surface proteins, so that the antibodies no longer recognize them. Boris can now safely proliferate without antibody interference,resulting in fever. As soon as the immune system rec-ognizes that there are new foreign proteins in theblood, it churns out a new set of antibodies that arespecific for Boriss new surface proteins. But Boris isready, and quickly changes his surface proteins again.This antigenic variation allows Boris to continue caus-ing relapses for many weeks. Figure 13-12 Diagnosis is made by drawing blood cultures (cultureon special media) during the febrile periods only (asblood cultures are often negative when the patient isafebrile). A Wrights or Giemsa-stained smear of pe-ripheral blood during febrile periods may reveal the Leptospira are found all over the world in the urine ofspirochete between red blood cells. Dark-field mi- dogs, rats, livestock, and wild animals. These spiro-croscopy is also useful. chetes can penetrate abraded skin or mucous mem- Doxycycline or erythromycin is the treatment of branes when humans come in contact with the urinechoice. either directly or by swimming in contaminated water LEPTOSPIRA (usually swallowed). Clinically, there are 2 phases. In the first or lepto- spiremic phase the bacteria invade the blood and CSF, Leptospira are long, thin aerobic spirochetes that are causing an abrupt onset of high spiking temperatures,wound up in a tight coil. They have a hook on one or both headache, malaise, and severe muscle aches (thighs andends, giving them an "ice tongs" appearance. Currently lower back). Classically, the conjunctiva are red and theLeptospira are divided into 2 species. One of them, Lep- patient experiences photophobia. After about 1 week,tospira interrogans, causes human disease and has been there is a short afebrile period and then the fever anddivided by serologic tests into 23 serogroups (sub- earlier symptoms recur. This second or immunegroups) and over 240 serovars (sub-subgroups). phase correlates with the appearance of IgM antibod- 99
  • 105. CHAPTER 13. SPIROCHETES ies. During the second phase patients may develop suits are available. To arrive at your diagnosis, youmeningismus, and the cerebrospinal fluid (CSF) exam must integrate the clinical history (animal contact orreveals an elevated white cell count in most patients. swimming in areas shared by animals), symptoms sug- Leptospira interrogans (classically serogroup ictero- gestive of leptospirosis, and lab tests reflecting the af-haemorrhagiae, but can be other serogroups) can cause fected organs (elevated liver function tests and proteina more severe illness called Weils disease, or infec- in the urine). Treat patients immediately with eithertious jaundice, which involves renal failure, hepatitis penicillin or doxycycline.with jaundice, mental status changes, and hemorrhagein many organs. Fig. 13-13. Summary of the spirochetes. References Diagnosis is made by culturing (on special media)blood and CSF during the first febrile phase. During thesecond phase and months later the organisms can becultured from the urine. Spach DH, et. al. Tick-borne diseases in the United States. N The only problem is that treatment should be initi- Engl J Med 1993;329:936-947.ated quickly, before any of the above diagnostic test re- 10 0
  • 106. ACID-FAST BACTERIA CHAPTER 14. MYCOBACTERIUMThe Mycobacteria include 2 species that almost every Persons infected with HIV lack the powerful cell-one has heard of: Mycobacterium tuberculosis, which mediated immunity necessary to combat tuberculosis.causes tuberculosis, and Mycobacterium leprae, which With the rise in HN infected persons, we are witness-causes leprosy. Humans are the only species infected ing a rise in tuberculosis. About 1I3 of HIV infectedwith these critters. These organisms are thin rods with persons worldwide also harbor Mycobacterium tubercu-lipid-laden cell walls. This high lipid content makes losis! You will confront this villain again and again inthem acid-fast on staining. Only Mycobacteria and No- your future career.cardia are acid-fast. This acid-fast bacillus (rod) is an obligate aerobe, In the acid-fast stain, a smear of sputum, for exam- which makes sense as it most commonly infects theple, is covered with the red stain carbolfuchsin and lungs, where oxygen is abundant. Mycobacterium tuber-heated to aid dye penetration. Acid alcohol (95% ethanol culosis grows very slowly, taking up to 6 weeks for visi-and 3% HCl) is poured over the smear, and then a ble growth. The colonies that form lump together due tocounter-stain of methylene blue is applied. The cell wall their hydrophobic lipid nature, resulting in clumpedlipids of the Mycobacterium do not dissolve when the colonies on agar and floating blobs on liquid media.acid alcohol is applied, and thus the red stain does notwash off. So acid-fast organisms resist decolorizationwith acid alcohol, holding fast to their red stain, whilebacteria that are not acid-fast lose the red stain andtake on the blue.Fig. 14-1. Visualize a fast red sports car to remem-ber that acid-fast organisms stain red. Figure 14-2 There is one class of lipid that only acid-fast or- ganisms have and that is involved in mycobacterial virulence-mycosides. The terminology is as follows: 1) Mycolic acid is a large fatty acid. Fig. 14-2. The chemical structure of mycolic acid, which is a large fatty acid. 2) Mycoside is a mycolic acid bound to a carbohy- Figure 14-1 drate, forming a glycolipid. 3) Cord factor is a mycoside formed by the union of 2 mycolic acids with a disaccharide (trehalose). This my- coside is only found in virulent strains of Mycobac- Mycobacterium tuberculosis (Tuberculosis) terium tuberculosis. Its presence results in parallel Worldwide, there are an estimated 10 million new growth of the bacteria, so they appear as cords. Exactlycases of tuberculosis and 3 million deaths from tuber- how the virulence occurs is still unknown, but experi-culosis annually. Tuberculosis is currently on the rise in ments show that cord factor inhibits neutrophil migra-the U.S., particularly involving the elderly (especially in tion and damages mitochondria. Its injection into micenursing homes), AIDS patients, and the urban poor. results in the release of tumor necrosis factor (TNF or 102
  • 107. CHAPTER 14. MYCOBACTERIUM Figure 14-3cachectin), resulting in rapid weight loss. Tuberculosis CORD (cord factor) attached to his leg (so as not to losein humans is usually a chronic disease with weight his stick). Notice Mike has a cough and some weight loss.loss that can be mistaken for the cachexia of malig-nancy. Cord factor might contribute to this weight lossphenomenon. Pathogenesis of Tuberculosis 4) Sulfatides are mycosides that resemble cord fac-tor with sulfates attached to the disaccharide: They in- Mycobacterium tuberculosis primarily affects thehibit the phagosome from fusing with the lysosome that lung but can also cause disease in almost any other tis-contains bacteriocidal enzymes. The facultative intra- sue. The way it spreads and damages the body dependscellular nature of Mycobacterium tuberculosis during on the hosts immune response. The organism and theearly infection may be partly attributable to the sul- immune system interact as follows:fatides (see Fig. 2-7). 5) Wax D is a complicated mycoside that acts as an 1) Facultative intracellular growth: With theadjuvant (enhances antibody formation to an antigen) first exposure (usually by inhalation into the lungs),and may be the part of Mycobacterium tuberculosis that the host has no specific immunity. The inhaled bac-activates the protective cellular immune system. teria cause a local infiltration of neutrophils and macrophages. Due to the various virulence factors, theFig. 14-3. To remember the names of the mycosides and phagocytosed bacteria are not destroyed. They multiplytheir relationship to Mycobacterium tuberculosis, picture and survive in the macrophages. The bacteria cruisethe surfing dude Mike (mycosides). He is WAXING (wax through the lymphatics and blood to set up camp in dis-D) his SUrfboard (sulfatides) and has his surfboard tant sites. This period of facultative intracellular exis- 10 3
  • 108. CHAPTER 14. MYCOBACTERIUMtence is usually short-lived because the host rapidly ac- 5 mm of induration in patients who are immunocom-quires its prime defense against the acid-fast buggers: promised, such as those with AIDS.cell-mediated immunity. Note that a positive test does not mean that the pa- 2) Cell-mediated immunity: Some of the tient has active tuberculosis; it indicates exposure andmacrophages succeed in phagocytosing and breaking infection to Mycobacterium tuberculosis at some timeup the invading bacteria. These macrophages then run in the past. A positive test is present in persons with ac-toward a local lymph node and present parts of the bac- tive infection, latent infection, and in those who haveteria to T-helper cells. The sensitized T-cells then been cured of their infection.multiply and enter the circulation in search of My- False positive test: You still must be wary with thiscobacterium tuberculosis. When the T-cells encounter test because some people from other countries have hadtheir antigenic target, they release lymphokines that the BCG (bacillus Calmette-Guerin) vaccine for tu-serve to attract macrophages and activate them when berculosis. This vaccine is debatably effective in pre-they arrive. These activated macrophages can now de- venting tuberculosis but it causes a positive PPD.stroy the bacteria. It is during this stage that the False negative test: Some patients do not react tomacrophage attack actually results in local destruction the PPD even if they have been infected with tubercu-and necrosis of the lung tissue. The necrosed tissue losis. These patients are usually anergic, whichlooks like a granular creamy cheese and is called means that they lack a normal immune response duecaseous necrosis. This soft caseous center is sur- to steroid use, malnutrition, AIDS, etc. To determinerounded by macrophages, multinucleated giant cells, whether a patient is anergic or just has not been in-fibroblasts, and collagen deposits, and it frequently cal- fected with tuberculosis, a second injection (either withcifies. Within this granuloma the bacteria are kept at Candida or mumps antigen) is given in the other arm.bay but remain viable. At some point in the future, per- Most people have been exposed to these antigens, sohaps due to a depression in the hosts resistance, the only individuals who are anergic will not respond tobacteria may grow again. the Candida or mumps injection with induration after 48 hours.PPD Skin Test Clinical Manifestations Following induction of cell-mediated immunity The first exposure to Mycobacterium tuberculosis isagainst Mycobacterium tuberculosis, any additional ex-posure to this organism will result in a localized de- called primary tuberculosis and usually is a subclini-layed-type hypersensitivity reaction (type IV cal (asymptomatic) lung infection. Occasionally, anhypersensitivity). Intradermal injection of antigenic overt symptomatic primary infection occurs.protein particles from killed Mycobacterium tuberculo- When an asymptomatic primary infection occurs, the acquired cell-mediated immunity will wall off andsis, called PPD (Purified Protein Derivative), results in suppress the bacteria. These defeated bacteria lie dor-localized skin swelling and redness. Therefore, intra-dermal injection of PPD will reveal whether or not a mant but can later rise up and cause disease. This sec-person has been infected with Mycobacterium tubercu- ond infection is called secondary or reactivationlosis. This is important because many infected individ- tuberculosis.uals will not manifest a clinical infection for years. For the real number crunchers, here are the statistics:When a positive PPD test occurs, you can treat and Close contacts, such as household members, of someoneeradicate the disease before it significantly damages the with pulmonary tuberculosis have a 30% chance of being infected. Of all the infected persons, about 5% will de-lungs or other organs. When you have a patient with a low-grade fever and velop tuberculosis in the next 1 or 2 years and 5% willcough, or a patient who has been in contact with people develop reactivation tuberculosis sometime later in life.who have tuberculosis (you, for example, after working So there is a 10% lifetime risk of developing tuberculosis for those infected with Mycobacterium the hospital), you will decide to "place a PPD." Youinject the PPD intradermally (just barely under the Primary Tuberculosisskin so that the skin bubbles up). Macrophages in theskin will take up the antigen and deliver it to the T- 1) Mycobacterium tuberculosis is usually transmit-cells. The T-cells then move to the skin site, release ted via aerosolized droplet nuclei from the aerosolizedlymphokines that activate macrophages, and within respiratory secretions of an adult with pulmonary tu-1-2 days the skin will become red, raised, and hard. A berculosis. This adult will shower the air with these se-positive test is defined as an area of induration (hard- cretions when he coughs, sings, laughs, or talks.ness) that is bigger in diameter than 10 mm after 48 2) The inspired droplets land in the areas of the lunghours (the time it takes for a type IV delayed hyper- that receive the highest air flow: the middle and lowersensitivity reaction to occur). The test is positive at lung zones. Here there will be a small area of pneu- 104
  • 109. CHAPTER 14. MYCOBACTERIUMmomtis with neutrophils and edema, just like any bac- 2) Symptomatic primary tuberculosis occurs farterial pneumonia. less frequently, more commonly in children, the elderly, 3) Now the bacteria enter macrophages, multiply, and the immunocompromised (especially HIV infectedand spread via the lymphatics and bloodstream to the persons). These groups do not have as powerful a cell-regional lymph nodes, other areas of the lungs, and dis- mediated immune system as do healthy adults, so thetant organs. organisms are not suppressed. Tuberculosis is a confusing disease because so many Fig. 14-5. Overt or manifest primary tuberculosis:different things can happen. As cell-mediated immunity Large caseous granulomas develop in the lungs or otherdevelops, 1) the infection can be contained so that the organs. In the lungs the caseous material eventuallypatient will not even realize he was infected, or 2) it can liquifies, is extruded out the bronchi, and leaves behindbecome a symptomatic disease. cavitary lesions, shown here with fluid in the cavities (called "cavitary lesions with air-fluid levels" on chest 1) Asymptomatic primary infection: The cell- X-ray).mediated defenses kick in, and the foci of bacteria be-come walled off in the caseous granulomas. These Secondary or Reactivation Tuberculosisgranulomas then heal with fibrosis, calcification, andscar formation. The organisms in these lesions are de- Most adult cases of tuberculosis occur after the bac-creased in number but remain viable. Tiny tubercles teria have been dormant for some time. This is called(as the granulomas are called) are often too small to be reactivation or secondary tuberculosis. The in-seen even on chest X-ray. Only a PPD will give the bug- fection can occur in any of the organ systems seededgers away. Sometimes the chest film will suggest recent during the primary infection. It is presumed that ainfection by showing hilar lymph node enlargement or temporary weakening of the immune system may pre-calcifications. cipitate reactivation. Many AIDS patients develop tu- berculosis in this manner. HIV infected patients whoFig. 14-4. A calcified tubercle in the middle or lower are infected with Mycobacterium tuberculosis have alung zone is called a Ghon focus. A Ghon focus accom- 10% chance/year of developing reactivation tuberculo-panied by perihilar lymph node calcified granulomas is sis! And 1 /s of HN infected persons are also infectedcalled a Ghon, or Ranke, complex. with Mycobacterium tuberculosis (worldwide)!Figure 14-4 Figure 14-5 105
  • 110. CHAPTER 14. MYCOBACTERIUM 5) Skeletal: This usually involves the thoracic and lumbar spine, destroying the intervertebral discs and then the adjacent vertebral bodies (Potts disease). 6) Joints: There is usually a chronic arthritis of 1 joint. 7) Central nervous system: Tuberculosis causes subacute meningitis and forms granulomas in the brain. 8) Miliary tuberculosis: Tiny millet-seed-sized tu- bercles (granulomas) are disseminated all over the body like a shotgun blast. The kidneys, liver, lungs, and other or- gans are riddled with the tubercles. A chest film will some- times show a millet-seed pattern throughout the lung. This disease usually occurs in the elderly and in children. BIG PICTURE: Tuberculosis is usually a chronic disease; it presents slowly with weight loss, low-grade fever, and symptoms related to the organ system infected. Because of its slow course, it may be confused with cancer. When- ever you have an infection of any organ system, tuberculosis will be somewhere on your differen- tial diagnosis list. It is one of the great imitators!Figure 14-6 Risk of Reactivation in all Persons: 10% for Lifetime! Diagnosis Risk of reactivation in HIV infected: 10% per year! 1) PPD skin test: This screening test indicates anFig. 14-6. The organ systems that can be involved in exposure sometime in the past.tuberculosis: 2) Chest X-ray: You may pick up an isolated gran- uloma, Ghon focus, Ghon complex, old scarring in the 1) Pulmonary tuberculosis: This is the most com- upper lobes, or active tuberculous pneumonia.mon site of reactivation tuberculosis. The infection usu- 3) Sputum acid-fast stain and culture: When theally occurs in the apical areas of the lung around the acid-fast stain or culture are positive, this indicates anclavicles. It normally reactivates in the upper lobe be- active pulmonary infection.cause oxygen tension is the highest there, due to de-creased pulmonary circulation, and Mycobacterium The treatment and control of tuberculosis is compli-tuberculosis is an aerobic bacterium. Slowly these areas cated and will be discussed in the mycobacterial antibi- otics chapter (see Chapter 18).of infection grow, caseate, liquify, and cavitate. Clini-cally, the patients usually present with a chronic low-grade fever, night sweats, weight loss, and a productive Tuberculosis "Rule of Fives"cough that may have blood in it. This slow erosive in-fection occurs as the host macrophages and T-cells bat- • Droplet nuclei are 5 micrometers and contain 5 My-tle to wall off the bacteria. cobacterium tuberculosis bacilli. 2) Pleural and pericardial infection: Infection in • Patients infected with Mycobacterium tuberculosisthese spaces results in infected fluid collections around have a 5% risk of reactivation in the first 2 years andthe lung or heart respectively. then a 5% lifetime risk. 3) Lymph node infection: Worldwide, this is the Patients with "high five" NW will have a 5+5% riskmost common extrapulmonary manifestation of tuber- of reactivation per year!culosis. The cervical lymph nodes are usually involved.They become swollen, mat together, and drain. Lymphnode tuberculosis is called scrofula. 4) Kidney: Patients will have red and white blood ATYPICAL MYCOBACTERIAcells in the urine, but no bacteria are seen by Gram stain A large group of mycobacteria live in water and soilor grow in culture (remember that Mycobacterium tuber- mostly in the southern U. S. Based on tuberculin reac-culosis takes weeks to grow in culture and are acid-fast). tions specific for these organisms (like the PPD), itThis is referred to as sterile pyuria. has been estimated that up to 50% of the southern 10 6
  • 111. CHAPTER 14. MYCOBACTERIUM Figure 14-7population have been infected subclinically. These bac- Pacific Islands (Hawaii included). Every year in theteria rarely produce an overt infection, and when they U.S. there are close to 200 newly diagnosed cases, usu-do, it is usually a pneumonia milder than pulmonary tu- ally in immigrants. It is unclear why some people are in-berculosis, or a skin granuloma or ulcer (see Fig. 14-11). fected and some are not. Many studies have attempted to infect human volunteers, with little success. Infection One particular organism in this group deserves occurs when a person (who for unknown reasons is sus-mention because it has become an important pathogen ceptible) is exposed to the respiratory secretions or, lessin AIDS patients. Mycobacterium avium-intracel- likely, skin lesions of an infected individual.lulare ( MAI), also called Mycobacterium avium-complex The clinical manifestations of leprosy are dependent(MAC), usually only infects birds (avium) and other ani- on 2 phenomena: 1) The bacteria appear to grow bettermals. It has now become one of the major systemic bac- in cooler body temperatures closer to the skin surface.terial infections of AIDS patients, usually late in the 2) The severity of the disease is dependent on the hostscourse of the disease. In fact, 50% of AIDS patients ex- cell-mediated immune response to the bacilli (whichamined at autopsy are found to be infected with MAI. It live a facultative intracellular existence, like Mycobac-is rarely the cause of death; however, it is certainly a terium tuberculosis).harbinger of death as it only strikes when the T-helpercount is virtually nonexistent (see Chapter 25). Infection Fig. 14-7. The acid-fast rod Mycobacterium leprae iswith MAI results in a chronic wasting illness; the bacte- seen here cooling off on an ice cube. Leprosy involves theria disseminate everywhere involving the liver, spleen, cooler areas of the body. It damages the skin (sparingbone marrow, and intestine. The intestinal involvment warm areas such as the armpit, groin, and perineum),often results in chronic watery diarrhea. the superficial nerves, eyes, nose and testes. Cell-mediated immunity once again plays an important Mycobacterium leprae role in the pathogenesis of this disease. The cellular im- (Leprosy, also called Hansens Disease) munity that limits the spread of the bacteria also causes inflammation and granulomas, particularly in skin and Like Mycobacterium tuberculosis, Mycobacterium nerves. Clinically, leprosy is broken up into five subdi-leprae is an acid-fast rod. It is impossible to grow this visions based on the level of cell-mediated immunity,bacterium on artificial media; it has only been grown in which modulates the severity of the disease:the footpads of mice, in armadillos, and in monkeys. Itcauses the famous disease leprosy. 1) Lepromatous leprosy (LL): This is the severest There are around 6 million persons infected with form of leprosy because patients canNOT mount a cell-Mycobacterium leprae worldwide, with cases focused in mediated immune response to Mycobacterium leprae. Itendemic areas such as India, Mexico, Africa, and the is theorized that defective T-suppressor cells (T-S cells) 10 7
  • 112. CHAPTER 14. MYCOBACTERIUMFigure 14-8Figure 14-9 108
  • 113. CHAPTER 14. MYCOBACTERIUMblock the T-helper cells response to the Mycobacterium is intact, so the lepromin skin test is usually positive.leprae antigens. The patient demonstrates localized superficial, uni-Fig. 14-8. Lepromatous leprosy (LL): The defeated lateral skin and nerve involvement. In this form of lep-macrophage is covered with Mycobacterium leprae acid- rosy, there are usually only 1 or 2 skin lesions. They arefast rods, demonstrating the very low cellular immunity. well-defined, hypopigmented, elevated blotches. TheThe patient with LL cannot mount a delayed hypersensi- area within the rash is often hairless with diminishedtivity reaction. LL primarily involves the skin, nerves, or absent sensation, and enlarged nerves near the skineyes and testes, but the acid-fast bacilli are found every- lesions can be palpated. The most frequently enlargedwhere (respiratory secretions and every body organ). The nerves are those closest to the skin-the greater auric-skin lesions cover the body with all sorts of lumps and ular, the ulnar (above the elbow), the posterior tibial,thickenings. The facial skin can become so thickened that and the peroneal (over the fibula head). The bacilli arethe face looks lionlike (hence, leonine facies). The nasal difficult to find in the lesions or blood. Patients are non-cartilage can be destroyed, creating a saddlenose de- infectious and often spontaneously recover.formity, and there is internal testicular damage (leading The 3 remaining categories represent a continuumto infertility). The anterior segment of the eyes can be- between LL and TL. They are called borderline lep-come involved, leading to blindness. Most peripheral romatous (BL), borderline (BB), and borderline tu-nerves are thickened, and there is loss of sensation in the berculoid (BT). The skin lesions of BL will be moreextremities in a glove and stocking distribution. The in- numerous and have a greater diversity of shape thanability to feel in the fingers and toes leads to repetitive those of BT.trauma and secondary infections, and ultimately contrac- The lepromin skin test is similar to the PPD usedtion and resorption of the fingers and toes. Lepromatous in tuberculosis. It measures the ability of the host toleprosy will eventually lead to death if untreated. mount a delayed hypersensitivity reaction against anti- gens of Mycobacterium leprae. This test is more prog- nostic than diagnostic and is used to place patients on 2) Tuberculoid leprosy (TL): Patients with TL the immunologic spectrum. It makes sense that TL pa-can mount a cell-mediated defense against the bacteria, tients would have a positive cell-mediated immune re-thus containing the skin damage so that it is not exces- sponse and thus a positive lepromin skin test, while LLsive. They will have milder and sometimes self-limiting patients, who cannot mount a cell-mediated immune re-disease. sponse, have a negative response to lepromin. See Chapter 18 for information about the treatmentFig. 14-9. Tuberculoid leprosy: The macrophage gob- of leprosy.bling up the Mycobacterium leprae acid-fast rodsdemonstrates the high cell-mediated resistance of tu- Fig. 14-10. The spectrum of leprosy.berculoid leprosy. The delayed hypersensitivity reaction Fig. 14-11. Summary of acid-fast bacteria. Tuberculoid Borderline Lepromatous Number of Single Several Many skin lesions Hair growth Absent Slightly Not affected on skin decreased l esions Sensation in Completely Moderately Not affected l esions of the lost l ost extremities Acid fast None Several I nnumerable bacilli in skin scrapings Lepromin Strongly No reaction No reaction skin test positive ( But a glove and stocking peripheral neuropathy, causing hand and feet numb- ness, is present!) Adapted from American Medical Association Drug evaluations, 6th edition, p. 1547. Figure 14-10 SPECTRUM OF LEPROSY 109
  • 114. Figure 14-11 ACID FAST BACTERIA M. Gladwin and 6. Trattler, Clinical Microbiology Made Ridiculously Simple ®MedMaster
  • 115. BACTERIA WITHOUT CELL WALLS CHAPTER 15. MYCOPLASMAThe Mycoplasmataceae are the tiniest free-living or- 1) Cold agglutinins: Certain antigens present onganisms capable of self-replication. They are smaller human red blood cells are identical to antigens of thethan some of the larger viruses. Mycoplasmataceae are Mycoplasma pneumoniae membrane glycolipids. Anti-unique bacteria because they lack a peptidoglycan cell bodies to these Mycoplasma pneumoniae antigens cross-wall. Their only protective layer is a cell membrane, react with human red blood cell antigens andwhich is packed with sterols (like cholesterol) to help agglutinate the red blood cells at 4°C. These antibodiesshield their cell organelles from the exterior environ- are thus called cold agglutinins. They develop by the first or second week of the Mycoplasma pneumoniae in-ment. Due to the lack of a rigid cell wall, Mycoplasmat-aceae can contort into a broad range of shapes, from fection, peak 3 weeks after the onset of the illness, andround to oblong. They therefore cannot be classified as slowly decline over a few months.rods or cocci. You can perform this simple test at the bedside. Put The lack of a cell wall explains the ineffectiveness of the patients blood in a nonclotting tube. After placingantibiotics that attack the cell wall (penicillin, this tube on ice, the blood will clump together if the pa-cephalosporin), as well as the effectiveness of the anti- tient has developed the cold agglutinin antibodies.ribosomal antibiotics erythromycin and tetracycline. Amazingly, when you lift the tube out of the ice, the There are 2 pathogenic species of Mycoplasmat- clumped blood will unclump as it warms in the palm ofaceae, Mycoplasma pneumoniae and Ureaplasma your hand.urealyticum. 2) Complement fixation test: The patients serum is mixed with glycolipid antigens prepared from My-Fig. 15- 1. Mycoplasmataceae surrounded only by a coplasma. A fourfold rise in antibody titer betweencell membrane, padded with sterols. Penicillin and acute and convalescent samples is diagnostic of a recentcephalosporin fail to tear down the cell membrane, infection.while they successfully destroy the cell wall of a nearby 3) Sputum culture: Mycoplasmataceae (both M.gram-positive Streptococcus. pneumoniae and U. urealyticum) can be grown on arti- ficial media. These media must be rich in cholesterol Mycoplasma pneumoniae and contain nucleic acids (purines and pyrimidines). After 2-3 weeks, a tiny dome-shaped colony of My- coplasma will assume a "fried-egg" appearance. Mycoplasma pneumoniae causes a mild, self-limited 4) Mycoplasma DNA probe: Sputum samples arebronchitis and pneumonia. It is the number one cause mixed with a labeled recombinant DNA sequence ho-of bacterial bronchitis and pneumonia in teenagers and mologous to that of the mycoplasma. The recombinantyoung adults. Following transmission via the respira- probe will label mycoplasma DNA if present.tory route, this organism attaches to respiratory ep-ithelial cells with the help of protein P1 (an adhesin This is a self-limiting pneumonia, but erythromycinvirulence factor). After a 2-3 week incubation period, and tetracycline will shorten the course of the illness. Ureaplasma urealyticuminfected patients will have a gradual onset of fever, sorethroat, malaise, and a persistent dry hacking cough.This is referred to as walking pneumonia, because ( T-strain Mycoplasma)clinically these patients do not feel very sick. Chest X-ray reveals a streaky infiltrate, which usu- Hold on!!! Why isnt this second species of Mycoplas-ally looks worse than the clinical symptoms and physi- mataceae called "Mycoplasma"? The man who namedcal exam suggest. Most symptoms resolve in a week, this tiny organism didnt want you to ever forget thatalthough the cough and infiltration (as seen on X-ray) Ureaplasma loves swimming in urine and producesmay last up to 2 months. Although Mycoplasma is a bac- urease to break down urea (so it is "urea-lytic"!). It isterium, the nonproductive cough and the streaky infil- sometimes referred to as a T-strain Mycoplasma, as ittrate on the chest X-ray are more consistent with a viral produces Tiny colonies when cultured.(atypical) pneumonia (see Chapter 12, page 83). Ureaplasma urealyticum is part of the normal flora Diagnostic tests include: in 60% of healthy sexually active women and commonly 111
  • 116. CHAPTER 15. MYCOPLASMA STREPTOCOCCAL PEPTIDOGLYCAN CELL WALL PENICILLIN Co STEROL PACKED Mycoplasma pneumoniae 0h CELL MEMBRANE PENICILLIN Figure 15-1infects the lower urinary tract, causing urethritis. Ure- Ureaplasma urealyticum can be identified by its abil-thritis is characterized by burning on urination (dy- ity to metabolize urea into ammonia and carbon dioxide.curia) and sometimes a yellow mucoid discharge from Fig. 15-2. Summary of the Mycoplasmataceae.the urethra. Neisseria gonorrhoeae and Chlamydia tra-chomatis are the other 2 bacteria that cause urethritis(see Chapter 12, page 80). 112
  • 117. I CHAPTER 15. MYCOPLASMA 113
  • 118. ANTI-BACTERIAL MEDICATIONS CHAPTER 16. PENICILLIN-FAMILY ANTIBIOTICS Figure 16-3 Fig. 16-3. Penicillin home. This looks like a house with a new room built on the side. Notice the funky antennaFigure 16-1 that run the groovy sound system. You will see later that changing the antennae, adding another antenna, or building a basement will create new types of penicillinSince its introduction during World War II, penicillin with differing spectrums of activity and potencies.has provided a safe and effective treatment for a multi-tude of infections. Over time, many bacteria have de-signed ways to defeat penicillin. Fortunately, scientists Mechanism of Actionhave continued to develop new types of penicillins, as The penicillins dont just slow the growth of bacteria,well as other antibiotics that are able to overcome most they kill bacteria. They are therefore bacteriacidal.of the bacterial defenses. You will recall (see Chapter 1) that both gram-posi.Fig. 16-1. This simple-looking box is a beta-lactam tive and gram-negative bacteria possess peptidoglycansring. All penicillin-family antibiotics have a beta-lactam in their cell walls. These are composed of repeating dis- accharide units cross-linked with amino-acids (pep-ring. For this reason they are also called the beta-lactam antibiotics. tides). The enzyme that catalyzes this linkage is called a transpeptidase.Fig. 16-2. Penicillin has another ring fused to the The penicillin must evade the bacterial defenses andbeta-lactam ring. penetrate the outer cell-wall layers to the inner cytoplas. mic membrane, where the transpeptidase enzymes are located. In gram-negative bugs, the penicillin must pass through channels known as porins. Then the penicillin beta-lactam ring binds to and competitively in- hibits the transpeptidase enzyme. Cell wall synthe- sis is arrested, and the bacteria die. Because penicillin binds to transpeptidase, this enzyme is also called the penicillin-binding protein. To be effective the beta-lactam penicillin must: 1) Penetrate the cell layers. 2) Keep its beta-lactam ring intact.Figure 16-2 3) Bind to the transpeptidase (penicillin-binding protein). 114
  • 119. CHAPTER 16. PENICILLIN-FAMILY ANTIBIOTICSResistance to Beta-Lactam Antibiotics Adverse Effects Bacteria defend themselves from the penicillin fam- All penicillins can cause anaphylactic (aller-ily in 3 ways. Gram-positive bacteria and gram-negative gic) reactions. An acute allergic reaction may occurbacteria use different mechanisms: from minutes to hours and is IgE-mediated. Bron- chospasm, urticaria (hives), and anaphylactic shock 1) One way that gram-negative bacteria defend (loss of ability to maintain blood pressure) can occur.themselves is by preventing the penicillin from pene- More commonly, a delayed rash appears several daystrating the cell layers by altering the porins. Remem- to weeks later.ber that gram-negative bacteria have an outer lipid All of the penicillin family antibiotics can cause diar-bilayer around their peptidoglycan layer (see Chapter rhea by destroying the natural GI flora and allowing re-1). The antibiotic must be the right size and charge to sistant pathogenic bacteria (such as Clostridiumbe able to sneak through the porin channels, and some dificile ) to grow in their place.penicillins cannot pass through this layer. Becausegram-positive bacteria do not have this perimeter de-fense, this is not a defense that gram-positives use. Types of Penicillin 2) Both gram-positive and gram-negative bacteria There are 5 types:can have beta-lactamase enzymes that cleave the C-Nbond in the beta-lactam ring. 1) Penicillin G: This is the original penicillin dis- covered by Fleming, who noted that the mold Penicil- lium notatum produced a chemical that inhibited Staphylococcus aureus. Penicillin was first used in hu- mans in 1941. 2) Aminopenicillins: These penicillins offer better coverage of gram-negative bacteria. 3) Penicillinase-resistant penicillins: This group is useful against beta-lactamase (an enzyme that destroys beta-lactam rings) producing Staphylococcus aureus. 4) Anti-Pseudomonal penicillins (including the carboxypemcillins, ureidopenicillins, and monobactams): This group offers even wider coverage against gram- negative bacteria (including Pseudomonas aeruginosa). 5) Cephalosporins: This is a widely used group of antibiotics that have a beta-lactam ring, are resistant to beta-lactamase, and cover a broad spectrum of gram- positive and gram-negative bacteria. Many bacteria produce cephalosporinases, making Figure 16-4 them resistant to many of these drugs.Fig. 16-4. Beta-lactamase enzyme (depicted here as a Penicillin Gcannon) cleaves the C-N bond. Fig. 16-5. Penicillin G is the original G-man of the Gram-positive bacteria (like Staphylococcus aureus) penicillins. There are oral dosage formulations of Peni-secrete the beta-lactamase (called penicillinase in cillin G, but it is usually given intramuscularly (IM) orthe secreted form) and thus try to intercept the antibi- intravenously TV. It is usually given in a crystallineotic outside the peptidoglycan wall. form to increase i ts half-life. Gram-negative bacteria, which have beta-lactamaseenzymes bound to their cytoplasmic membranes, de- Many organisms have now developed resistance tostroy the beta-lactam penicillins locally in the periplas- the old G-man because he is sensitive to beta-lactamasemic space. enzymes. But there are a few notable times when the G- man is still used: 3) Bacteria can alter the molecular structure of thetranspeptidase so that the beta-lactam antibiotic will 1) Pneumonia caused by Streptococcus pneumoniae.not be able to bind. Methicillin-resistant Staphylococcus (However, resistant strains are developing.)aureus ( MRSA) defends itself in this way, making it re- Penicillin V is an oral form of penicillin. It issistant to ALL of the penicillin family drugs. acid stable in the stomach. It is commonly given for 11 5
  • 120. CHAPTER 16. PENICILLIN-FAMILY ANTIBIOTICS Note that the aminopenicillins are one of the few drugs effective against the gram-positive enterococcus (see Fig. 16-17). Both ampicillin and amoxicillin can be taken orally, but amoxicillin is more effectively absorbed orally so you will frequently use it for outpatient treatment of bronchitis, urinary tract infections, and sinusitis, caused by gram-negative bacteria. IV ampicillin is commonly used with other antibiotics such as the aminoglycosides (gentamicin) for broad gram-negative coverage. In the hospital you will become very familiar with the "Amp-gent" combo! Patients with serious urinary tract infections are often infected with a gram-negative enteric or enterococcus. Amp-gent offers a perfect broad empiric coverage until cultures re- veal the exact organism responsible. Figure 16-6Figure 16-5streptococcus pharyngitis caused by group A beta-he- Penicillinase-Resistant Penicillinsmolytic streptococcus since it can be taken orally. Methicillin, nafcillin, and oxacillin are penicilli- nase-resistant drugs that can kill Staphylococcus au- reus. These are usually given IV.Aminopenicillins(Ampicillin and Amoxicillin) Methicillin was highly efficacious against staphylo- coccal infections, but because of the occurrence of inter- These drugs have a broader spectrum than Peni- stitial nephritis, its use has been discontinued in thecillin G, hitting more gram-negative organisms. This United States. You will still hear its name used fre-enhanced gram-negative killing is attributable to better quently in reference to sensitivity testing (e.g. Methi-penetration through the outer membranes of gram-neg- cillin Resistant Staphylococcus aureus).ative bacteria and better binding to the transpeptidase.However, like penicillin G, the aminopenicillins are still Fig. 16-6. This picture will help you remember theinhibited by penicillinase. names of the IV beta-lactamase resistant penicillins: The gram-negative bacteria killed by these drugs in- I met a nasty ox with a beta-lactamase ring aroundclude Escherichia coli and the other enterics (Proteus, its neck.Salmonella, Shigella, etc.). However, resistance has de-veloped: 30% of Haemophilus influenzae and many of Nafcillin is the drug of choice for serious Staphylo-the enteric gram-negative bacteria have acquired peni- coccus aureus infections, such as cellulitis, endocarditis,cillinase and are resistant. and sepsis. 11 6
  • 121. CHAPTER 16. PENICILLIN-FAMILY ANTIBIOTICS Fig. 16-8. Pseudomonas, which can cause a devastat- ing pneumonia and sepsis, is resistant to many antibi- otics. It is so crafty and sneaky that we need James Bond to help with its elimination. Bond is fortunate to have three excellent weapons for his task. He has his pick of a car (with special weapons and gadgets), a spe- cially trained tick that can home in on its target and suck out the life of the target, or a megaton pipe bomb: Carboxypenicillins: Ticarcillin and Carbenicillin Ureidopenicillins: Piperacillin and mezlocillin. Like ampicillin, these drugs are combined with an aminoglycoside to double up the Pseudomonas killing (synergism). Frequently used combos include "Pip and gent" and "ticar and gent." These drugs are sensitive to penicillinases, and thus most Staphylococcus aureus are resistant. Carbenicillin has certain disadvantages such as lower activity and thus the need for high dosages; high sodium load; platelet dysfunction; and hypokalemia. The parenteral form is currently not available for use in the United States. Replacement with ticarcillin or a ureidopeni- cillin has reduced these problems and provided antibac- terial activity.Figure 16-7. THE CLOX WERE TICKING. Beta-Lactamase Inhibitors ( Clavulanic Acid, Sulbactam, and Tazobactam)Fig. 16-7. The clocks (clox) were ticking. It was only These enzymes are inhibitors of beta-lactamase. Theya matter of time before the oral beta-lactamase re- can be given in combination with penicillins to create asistant penicillins were discovered: Cloxacillin and di- beta-lactamase resistant combination:cloxacillin. Amoxicillin and clavulanic acid = Augmentin There are now oral formulations of nafcillin and (trade name)oxacillin. Ticaricillin and clavulanic acid = Timentin These drugs are not good against gram-negative or- (trade name)ganisms. They are used for gram-positive bacteria, Ampicillin and sulbactam = Unasyn (trade name)especially those that produce penicillinase (Staphylo- Piperacillin and tazobactam = Zosyn (trade name)coccus aureus). These drugs provide broad coverage against the beta- When a patient has an infected skin wound (cellulitis, lactamase producing gram-positives (Staphylococcusimpetigo, etc.), you know he most likely has Staphylo- aureus), gram-negatives (Haemophilus influenza), andcoccus aureus or group A beta-hemolytic streptococcus. anaerobes (Bacteroides fragilis). The CephalosporinsTreating with Penicillin G, V, or ampicillin would notcover penicillinase-producing Staphylococcus aureus.Treating with one of these penicillinase-resistant agents There are now more than 20 different kinds ofwill, and if you give him one of the oral agents he can go cephalosporins. How do you become familiar with sohome on oral antibiotics. You wont have to take care of many antibiotics? Do not fear. This chapter will teachhim around the clock!!! you how to master these drugs!Anti-Pseudomonal Penicillins Fig. 16-9. The cephalosporins have 2 advantages over( Carboxypenicillins and Ureidopenicillins) the penicillins: This group of penicillins has expanded gram- 1) The addition of a new basement makes the beta-negative rod coverage, especially against the difficult- lactam ring much more resistant to beta-lactamasesto-destroy Pseudomonas aeruginosa. They are also ac- (but now susceptible to cephalosparinases!).tive against anaerobes (Bacteroides fragilis) and many 2) A new R-group side chain (another antenna-cablegram positives. TV if you will) allows for double the manipulations in 11 7
  • 122. CHAPTER 16. PENICILLIN-FAMILY ANTIBIOTICSFigure 16-8 Note that MRSA (Methicillin Resistant Staphylo- coccus aureus) is resistant to all cephalosporins be- cause it has changed the structure of its penicillin binding protein (transpeptidase). The Enterococci (in. cluding Streptococcus faecalis) are also resistant to cephalosporins . Fig. 16-11. MRSA and the Enterococci are resistant to the cephalosporins. A new cephalosporin has been classified as a fourth. generation antibiotic because it has great gram-negativeFigure 16-9 coverage like the 3rd generation but also has very good gram-positive coverage.the lab. This leads to all kinds of drugs with different The Names! How do you remember whichspectrums of activity. cephalosporin is in which group!!??!! The most impor- tant thing is to remember the trends and then you can There are 3 major generations of cephalosporins: look in any pocket reference book for the specific drugsfirst, second, and third. These divisions are based on in each group. However, it is nice to be familiar with thetheir activity against gram-negative and gram-positive names of individual drugs, and exams often expect youorganisms. to be able to recognize them. Here is an easy, althoughFig. 16-10. With each new generation of imperfect, way to learn many of them.cephalosporins, the drugs are able to kill an increasingspectrum of gram negative-bacteria. First-Generation At the same time, the newer cephalosporins are less Almost all cephalosporins have the sound cef in theireffective against the gram-positive organisms. The names, but the first generation cephalosporins are theStreptococci and Staphylococci are most susceptible to only ones with a PH. To know the first-generation cephalo.first-generation cephalosporins. sporins, you first must get a PH.D. in PHarmacology. 11 8
  • 123. CHAPTER 16. PENICILLIN-FAMILY ANTIBIOTICS Figure 16-10 cephalothin coats, and your FOXY cousin is drinking TEA in a toast cephapirin (Exceptions: cefazolin, cefadroxil) to your achievement. cephradine cephalexin cefamandole cefaclor Cefazolin is an important first-generation drug that cefuroxime ( Exceptions: cefmetazole, cefonicid, doesnt have a PH. Dont let this faze you! cefprozil, loracarbef) cefoxitin cefotetan (pronounced ce-fo-tea-tan) Second-Generation Third-Generation Fig. 16-12. Second-generation cephalosporins have fam, fa, fur, fox, or tea, in their names. After you get TRI for third (you know, triglycerides, etc.). Most of your PH.D., you would want to gather your family to the third-generation cephalosporins have a T (for tri) in celebrate! The FAMily is gathered, some wearing FUR their names. 119
  • 124. CHAPTER 16. PENICILLIN-FAMILY ANTIBIOTICS an acute IgE-mediated reaction or the more comm rash, which usually appears weeks later. "When do we use these antibiotics?" 1) First-generation cephalosporins: Recall Fig, 16-10 showing the excellent gram-positive coverage. First-generation cephalosporins are used as alterna- tives to penicillin for staphylococcal and streptococcal. infections when penicillin cannot be tolerated (allergy).. Surgeons love to give these drugs before surgery prevent infection from the skin.Figure 16-11 2) Second-generation cephalosporins: This group covers more of the gram-negative rods than the first-generation cephalosporins. Cefuroxime has good coverage against both Streptococcus pneumoniae and Haemophilus influenzae. This makes it an ideal agent for community-acquired bacterial pneumonia when the sputum is negative and you dont know what the organ- ism is. ( Streptococcus pneumoniae and Haemophilus in. fluenza are common causes of community-acquired pneumonia.) Cefuroxime is also good for sinusitis and otitis media, which are often caused by Haemophilus in- fluenza or Branhamella catarrhalis. Anaerobic coverage: Three second-generation cephalosporins cover anaerobic bacteria, such as Bac teroides fragilis. These can be used for intra-abdominal infections, aspiration pneumonias, and colorectal surgery prophylaxis, all of which involve anaerobic con- tamination from the GI tract. These 3 drugs are cefote- tan, cefoxitin, and cefmetazole Fig. 16-13. Some of the second-generation cephalo-Figure 16-12 sporins kill anaerobic bacteria, such as Bacteroides fragilis. Study the picture of a fox (cefoxitin) who met (cefmetazole) an anaerobic bug for tea (cefotetan).ceftriaxoneceftazidime (Exceptions: cefixime, cefoperazone, cefpodoxin, cefetamet) 3) Third-generation cephalosporins: These arecefotaxime used for the multi-drug resistant aerobic gram-negative or-ceftizoxime ganisms that cause nosocomial (hospital-acquired) pneu- monia, meningitis, sepsis, and urinary tract infections.ceftibuten The fourth generation cefepime is sometimes called anNote that cefotetan (tea) is a second generation drug. extended spectrum 3rd-generation cephalosporin. Think of him as the same but with a little added muscle againstFourth Generation gram-positives and the terrible Pseudomonas aeruginosa There is only one: Ceftazidime, cefoperazone, and cefepime are cefepime the only cephalosporins that are effective againstand it is the only cephalosporin with a fep in its name. Pseudomonas aeruginosa. So when you encounter the(Cefpirome is an investigational agent that will also "impossible-to-kill" Pseudomonas: Give it the Taz, thebelong in this class.) Fop, and the Fep! Ceftriaxone has the best CSF penetration and coversAdverse Effects the bacteria that frequently cause meningitis. It is the first-line drug for meningitis in neonates, children, and Ten percent of patients who have allergic reactions to adults. Ceftriaxone is also given IM for gonorrhea, aspenicillin will also have a reaction to cephalosporins. more Neisseria gonorrhoea have become resistant toSuch allergic reactions are the same as with penicillin: penicillin and tetracycline. 12 0
  • 125. CHAPTER 16. PENICILLIN-FAMILY ANTIBIOTICSFigure 16-13 Figure 16-14 121
  • 126. CHAPTER 1 6. PENICILLIN-FAMILY ANTIBIOTICS 1. Antipseudomonal penicillins 1. Penicillins with beta-lactamase inhibitor A. Ticarcillin A. Augmentin (Amoxicillin & clavulanate) B. Timentin (ticarcillin & clavulanate) B. Timentin (Ticarcillin & clavulanate) C. Piperacillin C. Unasyn (Ampicillin & sulbactam) D. Zosyn (piperacillin & tazobactam) D. Zosyn (Pipericillin & tazobactam) E. Carbenicillin 2. Second generation cephalosporins F. Mezlocillin A. Cefoxitin 2. Third generation cephalosporins B. Cefotetan A. Ceftazidime C. Cefmetazole B. Ceftizoxime 3. Imipenem and Meropenem C. Cefoperazone 3. Imipenem 4. Chloramphenicol 4. Aztreonam 5. Clindamycin 5. Quinolones 6. Metronidazole A. Ciprofloxacin 7. Trovafloxacin` B. Levofloxacin C. Trovafloxacin Figure 16-16 ANTIBIOTICS 6. Aminoglycosides A. Gentamicin THAT COVER THE ANAEROBES B. Tobramycin (INCLUDING BACTEROIDES C. Amikacin FRAGILIS) Figure 16-15 ANTIBIOTICS Clinical note: On the wards imipenem is called THAT COVER PSEUDOMONAS a "decerebrate antibiotic" because you dont have to think about what bacteria it covers. It covers almost everything!!! AER UGINOSA Meropenem is a newer carbapenem that is asImipenem powerful as imipenem. It can be used interchangeably. Meropenem is stable against dihydropeptidase, so There is now a new class of beta-lactam antibiotics calledthe carbapenems. You need to know one of its members... cilastin is not needed. Meropenem also has a reduced Tell yourself that you are a pen. Read: "Im a pen." potential for causing seizures in comparison with Now picture the pen crossing out all the bacteria that Imipenem.are difficult to treat. The pen (imipenem) can terminatealmost all of them. Aztreonam Imipenem has the broadest antibacterial activ- Aztreonam is a magic bullet for gram-negativeity of any antibiotic known to man!!! It kills gram- aerobic bacteria!!! It is a beta-lactam antibiotic, but itnegatives, gram-positives, and anaerobes (even tough is different in that it is a monobactam. It only has theguys like Pseudomonas aeruginosa and Enterococcus). beta-lactam ring, with side groups attached to the ring.Some bacteria that are still resistant to this drug include It does not bind to the transpeptidases of gram-positiveour enemy MRSA, some Pseudomonas species, and bac- or anaerobic bacteria, only to the transpeptidase ofteria without peptidoglycan cell walls ( Mycoplasma). gram-negative bacteria. Imipenem is stable to beta-lactamases. Because it is Fig. 16-14 A TREE (AzTREonam) has fallen throughvery small, it can pass through porin channels to the the center of our house, leaving only the square portionperiplasmic space. There it can interact with transpep- (beta-lactam ring) standing, and letting all the air intidase in a similar fashion as the penicillins andcephalosporins. Unfortunately, with heavy use of this (aerobic). You can imagine if this happened to your house it would be a negative (gram) experience. Aztre-antibiotic some bacterial strains have developed new onam kills gram-negative aerobic bacteria.enzymes that can hydrolyze imipenem, and some gram-negative bacteria have squeezed down their porin chan- Aztreonam kills the tough hospital-acquired, multi- nels to prevent its penetration. drug resistant, gram-negative bacteria, including The normal kidney has a dihydropeptidase that Pseudomonas aeruginosa. breaks imipenem down, so a selective enzyme inhibitor Data suggest there is little cross-reactivity with the of this dihydropeptidase is given with imipenem. The bicyclic beta-lactams, so we can use this in penicillin-al- inhibitor is cilastin. lergic patients! Imipenem can cause allergic reactions similar to those Clinical notes: Because this antibiotic only kills of penicillin. This drug also lowers the seizure threshold. gram-negative bugs, it is used (much like the aminogly- 122
  • 127. CHAPTER 16. PENICILLIN-FAMILY ANTIBIOTICS Methicillin-resistant Vancomycin Staph lococcus aureus (MRSA) Methicillin-resistant Vancomycin Staph lococcus epidermidis Enterococci 1. Ampicillin ( Group D Streptococci) 2. Vancomycin there is now emerging resistance to vancomycin 3. Imipenem and Meropenem 4. Piperacillin 5. Levofloxacin, Trovafloxacin,* Grepafloxacin,** and Sparfloxacin Figure 16-17 ANTIBIOTICS THAT COVER THE DIFFICULT- TO-KILL GRAM-POSITIVE BACTERIAcosides) along with an antibiotic that covers gram-posi- Recommended Review Articles:tives. The resulting combinations give powerful broad- Hellinger WC, Brewer NS. Carbapenems and Monobactams:spectrum coverage: Imipenem, Meropenem, and Aztreonam. Symposium on anti- vancomycin + aztreonam microbial agents. Mayo Clinic Proc 1999;74:420-434. clindamycin + aztreonam Marshall WF, Blair JE. The cephalosporins. Symposium on antimicrobial agents. Mayo Clin Proc 1999;74:187-195.Fig. 16-15. Antibiotics that cover Pseudomonas Wright, AJ. The penicillins. Symposium on antimicrobialaeruginosa. agents. Mayo Clinic Proc 1999;74:290-307.Fig. 16-16. Antibiotics that cover anaerobic bacteria, *Because of liver toxicity, the FDA advised thatincluding Bacteroides fragilis. trovafloxacin should be reserved for treatmentFig. 16-17. Antibiotics that cover the difficult-to-kill ONLY in patients that meet ALL of the followinggram-positive bacteria: methicillin-resistant Staphylo- criteria:coccus aureus ( MRSA), the enterococci, and methicillin- Who have been at least one of five types of serious andresistant Staphylococcus epidermidis. life threatening infections listed below that is judged by the treating physician to be serious and life or limb-Fig. 16-18. Summary of the penicillin (beta-lactam) threatening:family antibiotics. • Nosocomial pneumonia (pneumonia acquired in the • Community acquired pneumoniaReferences hospital)Fish DN, Singletary TJ. Meropenem, a new carbapenem an- • Complicated intra-abdominal infections, including tibiotic. Pharmacotherapy 1997; 17:644-669. • Gynecological and pelvic infectionsFraser KL, Grossman RF. What new antibiotics to offer in the post-surgical infections • Complicated skin and skin structure infections, in- outpatient setting. Sem Resp Infect 1998; 13:24-35.Gilbert DN, Moellering RC, Sande MA. The Sanford Guide to Antimicrobial Therapy 1998. 28th edition. Antimicrobial cluding diabetic foot infections Therapy Inc. Dallas Texas, 1998.Mandell GL, Bennett JE, Dollin R, eds. Principles and Prac- **The manufacturer has voluntarily withdrawn Grepa- tice of Infectious Diseases; 4th edition. New York: Living- floxacin from the market because of potential risk of stone 1995. cardiovascular events.Owens RC, Nightingale CH, et al. Ceftibuten: An overview. Pharmacotherapy 1997; 17:707-720.Rockefeller University Workshop. Special report: multiple- antibiotic-resistant pathogenic bacteria. N Engl J Med 1994;330:1247-1251. 123
  • 128. CHAPTER 17. ANTI-RIBOSOMAL ANTIBIOTICS Figure 17-2Figure 17-1 All cells depend on the continued production of proteins for growth and survival. Translation of mRNA into the polypeptides that make up these proteins requires the use of ribosomes. Antibiotics that inhibit ribosomal ac- tion would thus inhibit cellular growth and survival.Since we only want to inhibit the growth of pathogenicbacterial cells during an infection and not our own cells,we are fortunate that bacteria actually have a differenttype of ribosome than we do. We can exploit this differ-ence by specifically inhibiting the ribosomes of bacteria,while sparing the function of our own ribosomes. Bacte-rial ribosomes are smaller than ours. While we have an80S particle, the bacterial ribosome consists of a 70Sparticle that has 2 subunits: the 50S (large) and the 30S(small). (Surprisingly , 50S + 30S = 70S)Fig. 17-1. The bacterial ribosome. There are 5 important types of antibiotics that inhibitthe function of the bacterial ribosome. Three of them in-hibit the large 50S subunit, and the other two inhibitthe small 30S subunit. Heres how you can remember these 5 drugs:Fig. 17-2. Convert the ribosome to home plate andpicture a baseball player sliding into home. The ball isfielded by the catcher, who makes a CLEan TAG andthe player is out!!! Here is what CLEan TAG helps you Figure 17-3remember: C for Chloramphenicol and Clindamycin L for Linezolid Fig. 17-3. To remember which of these are orally ab- E for Erythromycin sorbed, we have drawn boxes around the CLEan TAG on T for Tetracycline the ribosome. Notice that the boxes do not extend AG for Aminoglycosides around the aminoglycosides (AG). We now draw a cakeNote that the word CLEan lies over the base and the with one-fourth missing-the same quadrant that isword TAG beneath the base. This corresponds to the ri- missing above. You can eat three quarters of the cake.bosomal subunit that these drugs inhibit: CLEan in- The fourth piece (representing the aminoglycosidehibits the 50S; TAG inhibits the 30S. quadrant) is missing, as this is the one anti-ribosomal 125
  • 129. CHAPTER 17. ANTI-RIBOSOMAL ANTIBIOTICSantibiotic that cannot be absorbed orally. The amino-glycoside must be given IM or IV for systemic treatmentof infections.Chloramphenicol( The "Chlorine") This drug has an amazing spectrum of activity. It isone of the few drugs (like Imipenem) that kills mostclinically important bacteria. It is like pouring"chlorine" on the organisms. Gram-positive, gram-neg-ative, and even anaerobic bacteria are susceptible. Itis one of the handful of drugs that can kill the anaerobicBacteroides fragilis.Clinical Uses Because of its rare but severe side effects, this other-wise excellent drug is used only when there is no alternateantibiotic, and thus the benefits far outweigh the risks: 1) It is used to treat bacterial meningitis, when theorganism is not yet known and the patient has severeallergies to the penicillins, including thecephalosporins. The wide spectrum of activity of chlo-ramphenicol and excellent penetration into the CSF willprotect this patient from the devastating consequencesof meningitis. 2) Young children and pregnant women who haveRocky Mountain spotted fever cannot be treated withtetracycline due to the side effects of tetracycline dis-cussed on page 128. Chloramphenicol then becomes thedrug of choice. Figure 17-4 Note: In under-developed countries this drug iswidely used. It only costs pennies and covers every-thing. Third world nations do not have the luxury of ex-pensive alternative drugs available in the U.S.Adverse EffectsFig. 17-4. Picture a can of chloramphenicol chlorine.Now picture the chlorine being poured down the shaft of along bone. You can well imagine that the bone marrowwould dissolve. This drug is famous for 2 types of bonemarrow depression. The first is dose-related and re-versible, and often only causes an anemia. The second typewipes out the bone marrow irreversibly and is usually fa-tal. This is called aplastic anemia. Aplastic anemiacaused by chloramphenicol is extremely rare, occurring inonly 1:24,000 to 1:40,000 recipients of the drug.Fig. 17-5. Now picture a baby who leaps into a freshlychlorinated pool. The baby crawls out of the pool, andthe chlorine has turned the babys skin gray ( GrayBaby Syndrome). Neonates, especially preemies, areunable to fully conjugate chloramphenicol in the liver orexcrete it through the kidney, resulting in very high Figure 17-5 12 6
  • 130. CHAPTER 17. ANTI-RIBOSOMAL ANTIBIOTICSblood levels. Toxicity occurs with vasomotor collapse(shock), abdominal distention, and cyanosis, which ap-pears as an ashen gray color.ClindamycinClinical Uses This drug is NOT useful against gram-negative bugs.So what is it good for? Many gram-positive bugs are in-hibited. So what? What else?!!!? Anaerobic infections! This is another of the rarehandful of antibiotics that cover anaerobes (includingBacteroides fragilis). Surgeons use clindamycin along Figure 17-6with an aminoglycoside for penetrating wound infec-tions of the abdomen, which may occur with bullet and Fig. 17-6. Visualize a VAN (vancomycin) and aknife trauma. When the GI tract is perforated, it re- METRO (metronidazole) cruising down the GI tract.leases its contents of gram-negative and anaerobic bugs They run over the ulcerative potholes of pseudomembra-into the sterile peritoneal cavity. The aminoglycosides nous colitis and kill the offending Clostridium dificile.cover the aerobic gram-negative organisms, and clin-damycin covers the anaerobes. Linezolid Clindamycin is also used for infections of the female ("The Godzilla Lizard")genital tract, such as septic abortions, as there are a lotof anaerobes there. Oral preparations of clindamycin Clinical Usesand vaginal cream are alternatives to metronidazole Linezolid, the Godzilla Lizard, is a newer antimicro-for the treatment of bacterial vaginosis. Topical clin- bial agent for stamping out resistant gram positivedamycin solution is also useful in the treatment of acne bugs. Linezolid blocks the 50S ribosomal subunit andvulgaris and rosacea (adult acne). thus has activity against gram positive organisms in- cluding those resistant to other antimicrobials. TheAdverse Effects Lizard will likely find a place as a last resort for van- You must know this: Clindamycin can cause comycin resistant enterococcus (VRE). Pseudomembranous Colitis!!!!! When you give a patient clindamycin, or another po- Adverse Effects tent antibiotic for that matter, it will destroy the nat- Headache occuring in 27% of patients and GI upset ural flora of the GI tract. Clostridium difficile, if (nausea, vomiting and diarrhea) in up to 18% of patients resistant to clindamycin, will grow like crazy and se- are the most common side effects seen to date. crete its exotoxin in the colon. This exotoxin causes ep- ithelial cell death and colonic ulcerations that are covered with an exudative membrane; thus the name Erythromycinpseudomembranous colitis. These patients often pre- ("A Wreath")sent with a severe diarrhea. Stool cultures yielding Clinical UsesClostridium dificile or titers of toxin found in the stoolcan help establish a diagnosis. Gram-positive organisms absorb erythromycin 100 Note: While clindamycin was first identified as the times better than do gram-negative bugs. It is inactivecause of pseudomembranous colitis, it is noteworthy against most gram-negatives. You will use this drug of-that other antibiotics also cause this condition. In fact ten, for it covers gram-positive bacteria, Mycoplasma,most cases are now caused by the penicillin fam- and the gram-negatives Legionella and Chlamydia, alsoily drugs because they are prescribed more frequently. known as atypicals. To treat pseudomembranous colitis, you must give oral Erythromycin is the drug of choice for community-ac-vancomycin or metronidazole. Vancomycin passes through quired pneumonia that does not require hospitalization.the GI tract without being absorbed and is therefore This is because it covers Streptococcus pneumoniae, My-highly concentrated upon reaching the colon. The high coplasma pneumoniae, and Chlamydia trachomatisconcentration can overwhelm and kill Clostridium diffi- (strain TWAR), all common causes of community-ac-cile. Metronidazole is less expensive and is now the quired pneumonia.preferred agent, because use of oral vancomycin may con- Erythromycin is often used as an alternative to peni-tribute to vancomycin resistant enterococcus! cillin for streptococcal and staphylococcal organisms in 12 7
  • 131. CHAPTER 17. ANTI-RIBOSOMAL ANTIBIOTICS Tetracycline/Doxycycline ("The Tet Offensive") Tetracycline chelates with cations in milk and milk products, aluminum hydroxide, Ca+, and Mg *. When it is chelated, it will pass through the intestine without being absorbed. Doxycycline is a tetracycline that chelates cations poorly and is thus better absorbed with food. IV tetracycline is no longer available. Clinical Uses of Doxycycline This drug is used for all the diseases you would expect a young soldier in the Tet offensive to get by crawling around in the jungle and mingling with prostitutes on leave: 1) Venereal diseases caused by Chlamydia tra- 2) Walking pneumonia caused by Mycoplasma pneu - chomatis. moniae ( used as an alternative to erythromycin).Figure 17-7 3) Animal and tick-borne diseases caused by Bru- cella and Rickettsia (see the ticks on the soldiers pantspenicillin-allergic patients, especially for strep throat in Fig. 17-8).and cellulitis. 4) Doxycycline also works wonders for acne.Fig. 17-7. Erythromycin is the drug of choice for Le- Adverse Effectsgionnaires disease (see Chapter 10). The heroicFrench foreign legionnaire has died in a desert battle. Fig. 17-8. Picture a Vietcong soldier involved in theIn his honor, a wreath is laid by his grave. Notice the Tet offensive to help remember these important sidetomb stone is in the shape of a cross to help you re- effects:member that erythromycin covers gram-positive organ- 1) This soldier is naturally very nervous as the Tet ofisms (and dont forget atypicals! Tomb stone courtesy of fensive involved waves of soldiers running into 20t-centuryDr. Cornejo, U. of Colorado). American fire power. So he has GI irritation with nausea,Adverse Effects vomiting, and diarrhea. This is a common side effect. 2) A grenade has blown up near him, burning his Erythromycin is one of the safest antibiotics, a skin like a sunburn. Notice the rays of light going frompretty wreath compared to that nasty chlorine. Its few the explosion to his face. Phototoxic dermatitis is aside effects include: skin inflammation on exposure to sunlight. 3) Shrapnel has struck his kidney and liver: renal 1) Common and dose-dependent abdominal pain and hepatic toxicity. These adverse effects are rare( GI irritation) resulting from stimulation of intestinal and usually occur in pregnant women receiving highperistalsis. doses by the intravenous route. 2) Rare cholestatic hepatitis. Imagine a wreath slip- 4) Note the dark discolored teeth of the into the bile duct and blocking flow. This drug will chelate to the calcium in the teeth and bones of babies and children under age 7, resulting in brown teeth and depressed bone growth. Dont give There are now new drugs in this class (the macrolide the drug to pregnant women or their babys teeth willantibiotics) such as: clarithromycin, azithromycin, look like those of the soldier.and roxithromycin. They are showing promise intreating the same bugs plus severe staphylococcal in- Aminoglycosidesfections, H. influenzae, and even coverage of some of theatypical mycobacterium (Mycobacterium avium-intra- (A Mean Guy) Azithromycin can be used as an alternative to doxycy-cellulare, MAI).cline for the treatment of (chlamydial) non-gonococcal ure- Aminoglycosides must diffuse across the cell wall to enthritis. It can be given as a single dose by mouth. It is also ter the bacterial cell, so they are often used with peni-used commonly to treat community acquired pneumonia. cillin, which breaks down this wall to facilitate diffusion. 12 8
  • 132. CHAPTER 17. ANTI-RIBOSOMAL ANTIBIOTICSFigure 17-8Clinical Uses trum and is good for hospital-acquired (nosocomial) in- fections that have developed resistance to other drugs In general, aminoglycosides kill aerobic gram-nega-. while doing time in the hospital.tive enteric organisms (the enterics are the bugs that 5) Neomycin has very broad coverage but is toocall the GI tract home, such as E. coli and company). toxic, so it can only be used topically for:The aminoglycosides are among the handful of drugs a) Skin infections.that kill the terrible Pseudomonas aeruginosa!!! 6) Netilmicin Most aminoglycosides end with -mycin: b) Preoperative coverage before GI surgery. This 1) Streptomycin is the oldest one in the family. drug is given orally before GI surgery as it cruisesMany bugs are resistant to it. down the GI tract, without being absorbed, killing 2) Gentamicin is the most commonly used of all the the local inhabitants. This prevents spilling of or-aminoglycosides. It is combined with penicillins to treat ganisms during surgery into the sterile peritonealin-hospital infections. There are also many bacterial cavity.strains resistant to this drug. Adverse Effects 3) Tobramycin is good against the terriblePseudomonas aeruginosa. Heres how we will remember the side effects: Picture 4) Amikacin does not end with mycin (sorry). this huge boxer, a mean guy (Aminoglycoside), andMaybe that is to set it apart. It has the broadest spec- now check out these pictures: 129
  • 133. CHAPTER 17. ANTIRIBOSOMAL ANTIBIOTICS Figure 17-10Figure 17-9Fig. 17-9. In the eighth round A MEAN GUY deliv-ers a crushing left hook to his opponents ear, hurlinghim off balance, ears ringing and head spinning (eighthcranial nerve toxicity: vertigo, hearing loss). The hear-ing loss is usually irreversible.Fig. 17-10. With his opponent off balance , Amean guysurges upward with a savage right hook into his left side, Figure 17-11pulverizing his kidney (renal toxicity). Aminoglycosidesare renally cleared and can damage the kidney. This canbe reversible, so always follow a patients BUN and crea-tinine levels, which increase with kidney damage. Spectinomycin (Spectacular Spectinomycin)Fig. 17-11. The opponent drops to the floor, out coldi n a complete neuromuscular blockade, unable to This drug has a name that sounds like an aminogly-move a muscle, or even breathe. This curare-like effect coside, but it is different structurally and rare. Its mechanism is similar in that it acts on the 30S ribo- Note: These side effects occur if the dose is very high, some to inhibit protein synthesis, but exactly how is notso when using these in the hospital, the drug level in the known. Group this with the aminoglycosides in theblood is checked after steady state levels have been CLEan TAG mnemonic (see Fig. 17-2) to remember itsachieved (usually after the third dose). With appropri- action, but note that it is NOT an aminoglycoside. It isate blood levels, these agents are generally safe. given as an IM injection. 13 0
  • 134. CHAPTER 17. ANTI-RIBOSOMAL ANTIBIOTICS discharge, you see tiny red (gram-negative) kidney- shaped diplococci inside the white blood cells. Now what? There are many penicillinase-producing and tetracycline-resistant Neisseria gonorrhoeae, but you still have a few antibiotics to chose from: 1) Ceftriaxone (a third generation cephalosporin): Give one shot IM in the butt! Also give doxycycline by mouth for 7 days to get the Chlamydia trachomatis that is hiding in the background in 50% of cases of urethritis! Azithromycin can be used as an alternative to doxycy- cline. It can be given as a single dose by mouth. Or: 2) Quinolone antibiotics (ciprofloxacin, ofloxacin) get Neisseria gonorrhoeae and are given as one oral dose (along with doxycycline for the Chlamydia). Or: 3) Spectinomycin: Give one shot in the butt! (along with doxycycline for the Chlamydia).Figure 17-12 Adverse EffectsClinical Uses Infrequent and minor. Spectinomycin does NOT cause the vestibular, cochlear, and renal toxicity that Spectinomycin is used to treat gonorrhea, caused by the aminoglycosides do.Neisseria gonorrhoeae, as an alternative to penicillinand tetracycline (doxycycline), since many strains are Fig. 17-14. Summary of anti-ribosomal antibiotics.resistant to these drugs.Fig. 17-12. Mr. Gonorrhoeae, resistant to tetracycline Recommended Review Articles:and penicillin. Alvarez-Elcoro S, Enzler MJ. The macrolides: Erythromycin, Clarithromycin, and Azithromycin. Symposium on antimi-Fig. 17.13. Spectacular spectinomycin treats resis- crobial agents. Mayo Clin Proc 1999;74:613-634.tant Neisseria gonorrhoeae. Edson RS, Terrell CL. The aminoglycosides. Symposium on antimicrobial agents. Mayo Clin Proc 1999;74:519-528. Lets briefly review the treatment of gonococcal ure- Kasten MJ. Clindamycin, Metronidazole, and Chlorampheni-thritis (gonorrhea) since this will incorporate a lot of the col. Symposium on antimicrobial agents. Mayo Clin Procdrugs we have studied. 1999;74:825-833. A patient presents with burning on urination and a Smilak, JD. The tetracyclines. Symposium on antimicrobialpurulent penile discharge. When you Gram stain the agents. Mayo Clin Proc 1999;74:727-729. Figure 17-13 13 1
  • 135. M. Gladwin and B. Trattler, Clinical Microbiology Made Ridiculously Simple ©MedMasterFigure 17-14 ANTI-RIBOSOMAL DRUGS
  • 136. CHAPTER 18. ANTI-TB and ANTI-LEPROSY ANTIBIOTICS Figure 18-1 TREATMENT OF TUBERCULOSIS teriocidal to Mycobacterium tuberculosis, but the risk of liver toxicity is too great if used for more than 2 months. This chapter will cover the first-line anti-tuberculosisantibiotics and the logical approach to their use. The first-line drugs, in order of their frequency of use, Treatment of PPD Reactorsare: These persons may have latent Mycobacterium tuber- Isoniazid (INH) "I saw a culosis in their bodies and might develop a reactivation Rifampin Red tuberculosis. Treatment of PPD reactors is th us pre- Pyrazinamide Pyre-BURNING THE ventive. Isoniazid is usually used alone for 6-12 LIVER" months as prophylactic therapy. Recently, a study Ethambutol showed that a 2 month course of rifampin plus pyrazi- Streptomycin namide was as effective as a 12 month course of isoniazid in PPD positive patients. This is important due to theFig. 18-1. Isoniazid ("I saw"), Rifampin ("red"), and high rate of non-compliance with a 12 month treatmentPyrazinamide ("pyre"), are first-line anti-tuberculosis regimen.antibiotics that can cause liver damage ("burning the Here is the difficulty: Not all persons who react to theliver"). PPD test should be treated. Some of these persons will When it comes to tuberculosis, you will encounter 2 never develop reactivation tuberculosis and the drugspopulations of patients: 1) those with active tuberculo- carry risks!!!sis and 2) those with a reactive PPD skin test, repre- The decision to treat PPD reactors involves balancingsenting a latent infection. These 2 populations are the risk of developing isoniazid-induced liver injurytreated very differently. against the risk of developing reactivation tuber- culosis. Imagine a set of scales. On one side weighs theTreatment of Active Tuberculosis ) risk of developing isoniazid-induced hepatitis and on the other side the risk of reactivating the disease tuberculosis. A patient presents with dyspnea, fever, productivecough, and night sweats that have lasted 2 months,along with upper lobe consolidation on chest X-ray. Risk of Isoniazid HepatitisAcid-fast bacilli are identified from a sputum sample. As indicated below, advancing age and alcohol con- A patient with active pulmonary or extra-pulmonary sumption increase the risk of developing hepatitis fromtuberculosis should receive a 6-month or 9-month treat- isoniazid and tip the scales towards not treating. No-ment as follows: tice that under the age of 35 there is virtually no risk of 6-month regimen: 2 months of isoniazid, rifampin, developing hepatitis with isoniazid:and pyrazinamide, followed by 4 months of isoniazidand rifampin. AGE % that develop HEPATITIS 9-month regimen: 9 months of isoniazid and <20 Rarerifampin. 20-34 <0.3% Notice that the 2 regimens differ in the inclusion or 35-49 < 1.2%exclusion of pyrazinamide. Pyrazinamide is rapidly bac- >50 <2.3% 133
  • 137. CHAPTER 18. ANTI-TB AND ANTI-LEPROSY ANTIBIOTICS Data from the Tuberculosis Advisory Committee re-port (1974). Isoniazid-Resistant Organisms Resistance to INH and the other antibiotics is devel- oping. This should be suspected in persons from Africa, Asia, or South America; homeless persons and others ex-Risk of Reactivation Tuberculosis posed to resistant organisms; and those whose sputum Factors that increase the risk of reactivation include cultures remain positive after 2 months of treatment.recent PPD conversion, having fibrotic scars on chest 1) Culture susceptibility testing should follow theX-ray, exposure to household members with active tu- initiation of treatment.berculosis, and being immunosuppressed. The larger 2) If resistance is suspected, 4 or more first-linethe skin reaction to PPD the more likely the test drugs should be used (INH, rifampin, pyrazinamide,is a true positive, representing M. tuberculosis ethambutol, or streptomycin).infection. Because. these factors increase the risk of re- 3) If resistance develops, never add a single new an-activation of tuberculosis, they will tip the scales to- tibiotic; always add two. This will insure that the re-wards treatment. sistant M. tuberculosis will be unable to develop further The Center for Disease Control and American resistance.Thoracic Society have used these concepts to formulatethe following recommendations for treating patients Note that there are now multiply resistant M. tu-with a 6-12 month course of prophylactic isoniazid: berculosis organisms that may require 4-5 different antibiotics.GREATEST RISK OF REACTIVATION: Treat the fol-lowing patients at any age if PPD >_ 5mm: DOT the Is and Cross the Ts to Prevent 1) Persons with HIV infection. Resistance!!! 2) Persons with fibrotic changes on chest X-ray com- DOT or Directly Observed Therapy: Health carepatible with old healed tuberculosis. providers in outpatient settings have their patients 3) Close contacts of persons with newly diagnosed ac- come into the clinic to receive their medications undertive tuberculosis. Note: In this case (especially with chil- direct observation to ensure adherence. Numerousdren), even if the PPD is negative, treat for 3 months, studies have now documented that this strategy canthen repeat the PPD. If at that time it is < 5mm, the decrease resistance and increase treatment efficacy.isoniazid may be discontinued.MODERATE RISK: Treat these patients at any age ifPPD 10mm: ANTI-TB ANTIBIOTICS Isoniazid, Rifampin, and Pyrazinamide: 1) Persons with medical conditions that lower 1) All cause hepatotoxicity: Patients on thesethe immune system, like diabetes, prolonged steroid medications must understand the symptoms of hepati-or immunosuppressive treatment, renal failure, and tis so they can report to a doctor immediately shouldothers. they develop. Mild elevations of liver enzymes can be ex- 2) Persons with recent skin test conversion within pected to occur in 15-20% of patients on isoniazid, butthe last 2 years. should these levels exceed 3-5x the upper limit of nor- mal, the drugs should be discontinued. 3) Persons who inject drugs. 2) All are absorbed orally: This is very important since these must be administered for 6-9 months. TheyLESS RISK: Treat these patients if age < 35 and must be orally absorbed!!!PPD 10mm: 3) All penetrate into most tissues: They must reach the center of caseous granulomas. High-risk populations such as the homeless, resi-dents of long-term care facilities, such as prisons andnursing homes, and foreign-born from countries with a Isoniazid (INH) ("I Saw")high-prevalence of tuberculosis. This is a great antibiotic because it is inexpensive, ab-LOWEST RISK: Treat at the physicians discretion if sorbed orally, and bacteriocidal. Were it not for the tox-age < 35: icity, it would be perfect!!! A person with no known risk factors and a PPD > INH interferes with the biosynthesis of the mycolic15mm. acid component of the cell wall of the Mycobacteria. 134
  • 138. CHAPTER 18. ANTI-TB AND ANTI-LEPROSY ANTIBIOTICSAdverse Effects 1) What do you think? Hepatotoxicity!!! Alcoholicsbeware! Alcohol increases the metabolism of INH by theliver, which increases the risk of developing hepatitisand decreases the therapeutic effect. 2) INH increases the urinary excretion and depletionof pyridoxine (vitamin B6), which is needed for propernerve function. INH will thus lead to decreased B6 lev-els, characterized by peripheral neuropathy, rash,and anemia. Many Docs routinely give Bs vitaminswith INH.Rifampin Figure 18-2!`Red") Think Rifampin: Pyrazinamide 1) Red: Body fluids such as urine, feces, saliva, ("Pyre")sweat, and tears are colored a bright red-orange color by The mechanism of action of pyrazinamide is notrifampin. This is not harmful to the patient, but pa- known.tients must be made aware of this or they will discon-tinue the medicine in a panic. Adverse Effects 2) RNA: Rifampin inhibits the DNA-dependent RNApolymerase of the Mycobacterium tuberculosis bugs. Pyrazinamide is hepatotoxic (no kidding?!) This med- icine is usually given for no more than 2 months to avoidAdverse Effects liver toxicity. Avoid it in pregnancy (unknown effect on fetus). 1) Hepatitis (much less than INH). 2) Rifampin induces the cytochrome P450 enzyme Ethambutolsystem (also called the microsomal oxidase system, or ("Ethane-Butane Torch")MOS), so many other drugs are gobbled up by thespruced-up MOS. This results in decreased half-lives Adverse Effectsof certain drugs in patients taking rifampin. Some Fig. 18-2. The main side effect of ethambutol is aexamples: dose-dependent, reversible, ocular toxicity. Think of an a) Coumadin (an anticoagulant): Blood-thinning effect will be reduced. ethane-butane flame torch, torching an eye. The ocu- b) Oral contraceptives: Women can get pregnant lar toxicity is manifested by: and get breakthrough bleeding! 1) Decreased visual acuity with loss of central vision c) Oral hypoglycemics and corticosteroids are less (central scotomata). effective. 2) Color vision loss. d) Anticonvulsants such as phenytoin (seizures!). Ethambutol is not used in young children because they are not able to report vision deterioration. AdultsRifabutin are tested for visual acuity and color perception at regular intervals. Many doctors instruct their pa- Rifabutin is very similar to rifampin in structure, an- tients to read the fine newspaper print everyday as atibacterial activity, metabolism, and adverse reactions. self exam.auium •intracellulare (MAI). MAI is usually more sensi-Itis commonly used in the treatment of Mycobacterium Streptomycintive to rifabutin than rifampin. The same drug-drug interactions of rifampin Streptomycin is in the aminoglycoside family, whichshould be considered for rifabutin however, rifabutin inhibits protein synthesis at the 30S ribosomal subunit,induces cytochrome P450 less than rifampin. Thus and is given IM or IV. It is ototoxic and nephrotoxic (seerifabutin is helpful in treating patients with tubercu- Chapter 17). Avoid it in pregnant women (can causelosis and HIV. congenital deafness). 135
  • 139. CHAPTER 18. ANTI-TB AND ANTI-LEPROSY ANTIBIOTICSFixed-Dose Combinations Fixed-dose combinations are available as Rifamate(isoniazid and rifampin) and Rifater (isoniazid, rifam-pin, and pyrazinamide). Such combinations are stronglyencouraged for adults who are self-administering theirmedications because they may enhance adherence, re-duce the risk of inappropriate monotherapy, and pre-vent drug resistance.Second-line Drugs These can be used when multiple antibiotics areneeded for the treatment of multi-drug resistant My-cobacterium. tuberculosis. Para-aminosalicyclic acid Capreomycin sulfate Cycloserine Ethionamide Kanamycin Amikacin (aminoglycoside) Quinolones such as ciprofloxacin and ofloxacin Treatment of LEPROSY Three drugs are used in the treatment of leprosy: dap-sone, rifampin, and clofazimine. The Rap Zone of Dapsone Wheres your ears? Figure 18-3 There on the floor. Wheres your hand? I left it on the door. Come on Doe, look and see, Less severe cases are treated with rifampin and dap. these rappin clowns got leprosy. sone for 6 months. See anti-tuberculosis medications (page 134), for Hey, you clown! more on rifampin. See the sulfa drugs (Chapter 19) for You left your nose in the car, more on dapsone. Hey, you clown! You left your toes in a bar, Call the doc, to the Rap Zone, Clofazimine Your first-line drug remains dapsone. Fig. 18-3. A clown-faced clown climbs a DNA double And if you dance to this stupid rappin, helix stairway. His outfit is colored red and black: watch your feet as they start a stampin, Theres only one thing to help your dancin, 1) Clofazimine works by binding to the DNA of My Time to reach for the drug, rifampin. cobacterium Leprae. It also has anti-inflammatory Their peelin clown faces look really lean. actions that are helpful in treating the leprosy Theyre healing faster than can be seen, reactions. As long as they stay close to clofazimine. 2) Clofazimine is a red-colored compound, and when it deposits in the skin and conjunctiva, it colors these Severe cases of leprosy should be treated with ri- tissues red. Any place on the body where there is a lep-fampin, dapsone, and clofazimine for a minimum of 2 rosy lesion, the skin will appear tan to black. Note theyears and until patients are acid-fast bacilli negative. clowns red and black outfit. 13 6
  • 140. CHAPTER 18. ANTI-TB AND ANTI-LEPROSY ANTIBIOTICSLeprosy Reactions nisone or clofazimine. However, the treatment of choice is thalidomide. This is the only use of thalidomide that Fifty percent of patients treated for leprosy develop a is condoned in the U.S. because it is a potent teratogen.leprosy reaction. There are 2 types (1 and 2) and both Again, the anti-leprosy antibiotics are NOT to be with-are immune-mediated, possibly in response to the in- drawn!crease in dead organisms with treatment. The reactionsinvolve inflammation of the nerves, testicles, eyes, Fig. 18-4. Summary of antibiotics for Mycobacteria.joints, and skin (erythematous nodules). Type 1 reactions occur only in borderline patients References( BT, BB, BL), and almost always occur during the firstyear of treatment. The skin lesions of leprosy typically Hopewell PC, Bloom BR. Tuberculosis and other Mycobacter-swell, becoming more edematous, and occasionally ul- ial Diseases. In: Murray JF, Nadel JA, eds. Textbook of Res- piratory Medicine. 2nd ed. Philadelphia: W.B. Saunders Co.cerate. Neuritis can also occur, leading to sensory or mo- 1994:1094-1160.tor nerve loss. The type 1 reaction is thought to be a Isoniazid-associated hepatitis: summary of the report of Tu-delayed hypersensitivity reaction to the dead bacilli. berculosis Advisory Committee and special consultants toWhen this reaction occurs, patients can be treated with the director, Centers for Disease Control. MMWR 23:97-98,prednisone or clofazimine. It is important that you do 1974.NOT withdraw the anti-leprosy drugs if a leprosy reac- U.S. Department of Health and Human Services, Division oftion occurs. Tuberculosis Elimination, Centers for Disease Control and Type 2 reaction (called Erythema Nodosum Lep- Prevention, American Thoracic Society. Core Curriculumrosum) is associated with borderline lepromatous (BL) on Tuberculosis: What the clinician should know. 3rd Edi-and lepromatous leprosy (LL). Commonly, a painful tion. Atlanta, Georgia, 1994.nodular rash erupts in a previously normal-appearing Van Scoy, Robert, M.D., Wilkowske, Conrad, M.D.; Antituber- culous Agents; Mayo Clin Proc 67:179-187, 1992.area of skin, along with a high fever. Neuritis, orchitis,arthritis, iritis, and lymphadenopathy can occur as well.The type 2 reaction is thought to be an immune com- Recommended Review Article: plex-mediated reaction involving the deposition of the Van Scoy RE, Wilkowske CJ. Antimycobacterial therapy. i mmune complexes in tissues followed by complement Symposium on antimicrobial agents. Mayo Clin Proc 1999; activation. These patients can also be treated with pred- 74:1038-1048.
  • 141. Figure 18-4 ANTIBIOTICS FOR MYCOBACTERIUM M. Gladwin and B. Trattler, Clinical Microbiology Made Ridiculously Simple ©MedMaster
  • 142. CHAPTER 19. MISCELLANEOUS ANTIBIOTICS Figure 19-1 evolution of quinolone structures now allow their classification into first, second, third and fourth gen- THE FLUOROQUINOLONE erations, with nalidixic acid solely in the first gener- ANTIBIOTICSCiprofloxacin and Family ation. Classification by generation is available on page 143. This relatively new group of antibiotics is expanding.The fluoroquinolones has become as large and impor-tant a group as the penicillins and cephalosporins. The Resistance to the Fluoroquinolonesreason for this is that they are safe, achieve high blood Like all antibiotics, with this excessive use, resis-levels with oral absorption, and penetrate extremely tant organisms are rapidly spreading. What makeswell into tissues. this particularly disconcerting is that the resistance is against all the fluoroquinolones. Resistance isFig. 19-1. All the antibiotics in the fluoroquinolone caused by a point mutation in the bacterial DNA gy-family have the common ending -FLOXACIN. To help rase subunits. This powerful new family of antibi-you remember some facts about this drug family, think otics should be used carefully to reduce the spread ofof a crazy naked group of partyers, a FLOCK OF SIN- resistance.NERS. They are all gyrating their hips as they partyand dance. The fluoroquinolones act by inhibiting DNA Adverse Effectsgyrase, resulting in the breakage of the bacterial DNA There are very few:structure. In the basic quinolone structure, the main feature 1) Some patients experience GI irritability (nausea,that distinguishes the fluoroquinolones from their vomiting, belly pain, diarrhea), as occurs with ery-predecessor, nalidixic acid, is the addition of a fluo- thromycin and doxycycline. The flock of sinners oftenrine group, hence the name fluoroquinolone. The vomit after their excessive drinking. 139
  • 143. CHAPTER 19. MISCELLANEOUS ANTIBIOTICSsuch as Staphylococcus aureus, gram-negatives includingPseudomonas aeruginosa (see Figure 16-15), and evenanaerobes such as Bacteroides fragilis. Add the treasure-trove to your list of GORILLA-CILLINS!!! Unfortunatelythe pirate who buried the treasure left behind a boobytrap that exploded when we opened the trove! *Because of liver toxicity, the FDA advised thattrovafloxacin should be reserved for treatment ONLY inpatients that meet ALL of the following criteria: Who have at least one of five types of serious andlife threatening infections listed below that is judged Figure 19-3by the treating physician to be serious and life orlimb-threatening: latter, which follows rapid infusion of vancomycin , there Nosocomial pneumonia (pneumonia acquired in the is often a nonimmunologic release of histamine, result- ing in a red rash of the torso and itching skin. Slow in- • Community acquired pneumonia hospital) fusion over an hour or antihistamine premedication can • Complicated intra-abdominal infections, including prevent this problem. post-surgical infections Vancomycin inhibits the biosynthesis of the gram- Gynecological and pelvic infections positive peptidoglycan at a step earlier than penicillin. Complicated skin and skin structure infections, in- It complexes with D-alanine D-alanine to inhibit cluding diabetic foot infections transpeptidation. Like penicillin, it acts synergisti- cally with the aminoglycosides. **The manufacturer has voluntarily withdrawn Vancomycin is not absorbed orally. We take ad- Grepafloxacin from the market because of potential vantage of this in the treatment of Clostridium dificile risk of cardiovascular events. pseudomembranous colitis. Vancomycin is taken orally, Sparfloxacin has two important side effects that set cruises down the GI tract unabsorbed, and kills theit apart: Clostridium dificile!! With the extensive use of vancomycin, new strains 1) Up to 8% of patients develop mild to severe of multiple drug-resistant gram-positive organismsphotosensitivity. have emerged (see page 27). Synercid (quinopristin/ 2) It can prolong the Q-T interval on the EKG, dalfopristin) is a new type of antibiotic that has a widewhich can predispose a patient to the arrhythmia Tor- spectrum of activity. It appears to be effective againstsades de pointer. 1 most of the multiple drug-resistant strains. VANCOMYCIN Linezolid is another new type of antibiotic in a to- tally new class of agents with activity against gram- positive organisms, including those resistant to other This IV antibiotic has a critical role in the treatment antimicrobials (see Chapter 17). ANTIMETABOLITESof infectious diseases. It is the opposite of aztreonam,which covers all gram-negative bugs. Vancomycin Trimethoprim and Sulfamethoxazolecovers ALL GRAM-POSITIVE bugs!!! Even MRSA (methicillin resistant Staphylococcusaureus)!! Nucleotide and DNA formation require tetrahydrofo- Even the Enterococcus ( Streptococcus faecalis)!! Even multi-resistant Staphylococcus epidermidis (in late (TH4). Bacteria make their own TH4 and use Parainfections of indwelling intravenous catheters). Amino Benzoic Acid (PABA-you know, the stuff in sun- It is also used to treat endocarditis caused by Strepto- screen) to make part of the TH4. People dont make TH4; we get it as a vitamin in our diet.coccus and Staphylococcus in penicillin-allergic patients. Fig. 19-4. The Sulfa drugs look like PABA.Fig. 19-3. A VAN with a + on its side (an ambulancevan) is driving out of some IV tubing. It is about to run When you give a person one of the sulfa drugs (e.g., sul-over an ear and hit a peptidoglycan cell wall. The famethoxazole), the bacteria use it, thinking its PABA.VAN is being driven by an Indian, the red man. This (There isnt much room for higher cortical neurons in apicture helps us remember that VANCOMYCIN is given single-celled creature.) The sulfa drug competitively in-N, kills gram-positive bugs by inhibiting peptidoglycan hibits production of TH4. Since our cells dont make TH4,production, and cause the red man syndrome. In the it doesnt affect us, but it affects the bacteria. 14 1
  • 144. CHAPTER 19. MISCELLANEOUS ANTIBIOTICS Figure 19-4 TH4 gives up carbons to form purines and other meta- T (Tree): Respiratory tree. TMP/SMX covers Strepto-bolic building blocks. After giving up a carbon, it be- coccus pneumoniae and Haemophilus influenzae. It iscomes dihydrofolate (TH2) and must be reduced back good for otitis media, sinusitis, bronchitis, and pneumo-to TH4 by the enzyme dihydrofolate reductase. nia, which are frequently caused by these bugs.Trimethoprim looks like the dihydrofolate reductase of M (Mouth): Gastrointestinal tract. TMP/SMX coversbacteria and competitively inhibits this reduction. This gram-negatives that cause diarrhea such as Shigella,inhibits bacterial DNA formation. Salmonella, and Escherichia coli. The big picture here is that trimethoprim P (PEE): Genitourinary tract. TMP/SMX covers uri-(TMP) and sulfamethoxazole (SMX) act synergis- nary tract infections, prostatitis, and urethritis causedtically to kill many gram-positive and gram-nega- by the Enterics (Escherichia coli and clan).tive bacteria. They both inhibit TH4 production SMX (Syndrome): AIDS. TMP/SMX covers Pneumo-but at different steps. cystis carinii pneumonia (PCP). It is given to prevent PCP when CD4+ T-cell counts drop below 200-250.Pharmacokinetics More than 60% of PCP infections are being prevented Oral absorption: Just imagine eating a big chunk of with this prophylactic intervention! It is also given in- travenously in high doses for active pneumonia.rotten egg which smells like sulfur. In addition to Pneumocystis carinii, other protozoans Excretion: Because it is excreted in the urine, this is covered by TMP/SMX are Toxoplasma gondii anda good drug for urinary tract infections. To remember Isospora belli.this, think of the pungent smell of sulfur, that rotten eggsmell, and then think of the pungent smell of urine Fig. 19-5. Summary of the miscellaneous antibiotics.when you walk by a Porta-Potti at a construction site.Make this smell association, and you wont forget. References Fraser KL, Grossman RF. What new antibiotics to offer in theAdverse Effects outpatient setting. Seminars on Respiratory Infections. 1998;13:24-35. Adverse effects are rare in persons without AIDS. Frieden TR, Mangi RJ. Inappropriate use of oral ciprofloxacin.They include nausea, vomiting, diarrhea, and skin JAMA 264:1438-1440,1990.rashes (drug eruptions). Approximately half of persons Gilbert DN, Moellering RC, Sande MA. The Sanford Guide towith AIDS develop adverse effects on TMP/SMX, in- Antimicrobial Therapy 1998. 28th Edition. Antimicrobialcluding skin rashes and bone marrow suppression. Therapy Inc., Dallas Texas 1998. Giving TMP/SULFA to a patient on warfarin blood thin- Martin SJ, Meyer JM, et al. Levofloxacin and Sparfloxacin: Newner is very dangerous! This drug interaction increases war- quinolone antibiotics. Ann Pharmacother 1998;32: 320-36.farin levels, resulting in a high risk of bleeding. Recommended Review Articles:Clinical Uses Smilack JD. Trimethoprim-Sulfamethoxazole. Symposium on Antimicrobial Agents. Mayo Clin Proc 74:730-734, 1999. TMP/SMX has no anaerobic coverage, but does have Walker RC. The Fluoroquinolones. Symposium on Antimicro-a wide gram-negative and gram-positive coverage (and bial Agents. Mayo Clin Proc 74:1030-1037, 1999.even covers some Protozoans). Study the following Wilhelm MP, Estes L. Vancomycin. Symposium on Anti-mnemonic TMP SMX: microbial Agents, Mayo. Clin Proc 74:928-935, 1999. 142
  • 145. M. Gladwin and B. Trattler, Clinical Microbiology Made Ridiculously Simple OMedMasterFigure 19-5 MISCELLANEOUS ANTIBIOTICS
  • 146. PART 2. FUNGI CHAPTER 20. THE FUNGIAs "budding" doctors in the modern world of AIDS, or- Cell wall: Surrounding the cell membrane is the cellgan transplantation, and modern chemotherapy, you wall, composed mostly of carbohydrate with some pro-will treat an unprecedented number of immunocompro- tein. Fungal cell walls are potent antigens to the humanmised patients. With their lowered cell-mediated im- immune system.munity, there is a dramatic increase in the incidence of Capsule: This is a polysaccharide coating that sur-virtually every fungal infection! You will commonly see rounds the cell wall. This antiphagocytic virulence fac-fungi that used to be exceedingly rare. tor is employed by Cryptococcus neoformans. The Fungi are eucaryotic cells, which lack chlorophyll, so capsule can be visualized with the India ink stain.they cannot generate energy through photosynthesis.They do require an aerobic environment. After dis- Fig. 20-1. It is helpful to organize the human fungalcussing the following crucial terms, we will discuss the diseases by the depth of the skin that they infect.categories of fungi pathogenic to humans. Yeast: Unicellular growth form of fungi. Thesecells can appear spherical to ellipsoidal. Yeast repro-duce by budding. When buds do not separate, they can SUPERFICIAL FUNGAL INFECTIONSform long chains of yeast cells, which are called Pityriasis versicolor and tinea nigra are ex-pseudohyphae. Yeast reproduce at a slower rate than tremely superficial fungus infections, whose pri-bacteria. mary manifestation is pigment change of the skin. Hyphae: Threadlike, branching, cylindrical, tubules Neither of these cause symptoms and will only comecomposed of fungal cells attached end to end. These to your attention because skin pigment change isgrow by extending in length from the tips of the tubules. noted!!! Both are named for their respective skin Molds (also called Mycelia): Multicellular colonies manifestations:composed of clumps of intertwined branching hyphae.Molds grow by longitudinal extension and produce Pityriasis versicolor ( multicolored)spores. Tinea nigra (black colored) Spores: The reproducing bodies of molds. Spores arerarely seen in skin scrapings. 1) Pityriasis versicolor (also called tinea versi- Dimorphic fungi: Fungi that can grow as either ayeast or mold, depending on environmental conditions color) is a chronic superficial fungal infection whichand temperature (usually growing as a yeast at body leads to hypopigmented or hyperpigmented patchestemperatures). on the skin. With sunlight exposure the skin around the Saprophytes: Fungi that live in and utilize organic patches will tan, but the patches will remain white. Thismatter (soil, rotten vegetation) as an energy source. infection is caused by Malassezia furfur. 2) Tinea nigra is a superficial fungal infection that FUNGAL MORPHOLOGY causes dark brown to black painless patches on the soles of the hands and feet. This infection is caused by Ex- Certain morphologic characteristics serve as viru- ophiala werneckii.lence factors as well as targets for antifungal antibi-otics. Diagnosis of both infections is based on microscopic Cell membrane: The bilayered cell membrane is the examination of skin scrapings, mixed on a slide withinnermost layer around the fungal cytoplasm. It con- potassium hydroxide (KOH). This will reveal hyphaetains sterols (sterols are also found in the cell mem- and spherical yeast, as the KOH digests nonfungalbranes of humans as well as the bacteria Mycoplasma). debris. Malassezia can look like spaghetti (hyphae) withErgosterol is the essential sterol in fungi, while cho- meatballs (spherical yeast).lesterol is the essential sterol in humans. The antibi- Treatment of both consists of spreading dandruffotics amphotericin B and nystatin bind to ergosterol shampoo containing selenium sulfide over the skin.and punch holes in the fungal cell membrane, while ke- This is an inexpensive and effective treatment. The top-toconazole inhibits ergosterol synthesis. ical antifungal imidazoles can also be used. 144
  • 147. CHAPTER 20. THE FUNGI Figure 20-1CUTANEOUS FUNGAL INFECTIONS of 2) Tinea cruris (jock itch): Patients develop itchy the SKIN, HAIR, and NAILS red patches on the groin and scrotum. 3) Tinea pedis (athletes foot): This infection com-The Dermatophytoses monly begins between the toes, and causes cracking and peeling of the skin. Infection requires warmth and mois- Dermatophytoses are a category of cutaneous fungal ture, so it only occurs in those wearing shoes.infections caused by more than 30 species of fungi. The 4) Tinea capitis (scalp): This condition primarilydermatophytic fungi live in the dead, horny layer of the occurs in children. The infecting organisms grow in theskin, hair, and nails (cutaneous layer seen in Fig. 20-1). hair and scalp, resulting in scaly red lesions with loss ofThese fungi secrete an enzyme called keratinase, which hair. The infection appears as an expanding ring.digests keratin. Since keratin is the primary structural 5) Tinea unguium (onychomycosis) (nails): Theprotein of skin, nails, and hair, the digestion of keratin nails are thickened, discolored, and brittle.manifests as scaling of the skin, loss of hair, and crum- The common dermatophytes include Microsporum,bling of the nails. To diagnose a dermatophyte infection:Trichophyton, and Epidermophyton. 1) Dissolve skin scrapings in potassium hydroxide 1) Tinea corporis (body): Following invasion of the (KOH). The KOH digests the keratin. Microscopic ex-horny layer of the skin, the fungi spread, forming a ring amination will reveal branched hyphae.shape with a red, raised border. This expanding raised 2) Direct examination of hair and skin with Woodsred border represents areas of active inflammation with light (ultraviolet light at a wavelength of 365nm). Cer-a healing center. This is appropriately called ringworm, tain species of Microsporum will fluoresce a brilliantsince it looks like a ring-shaped worm under the skin. green. 145
  • 148. CHAPTER 20. THE FUNGI The first-line drugs for treatment of dermatophy- Sporothrix schenckiitoses are the topical imidazoles. The skin should be (Sporotrichosis)kept dry and exposed to the drying effects of the air(nudity has its advantages!!). Oral griseofulvin is used Fig. 20-2. Spore tricks. Sporothrix schenckii is a di-with tinea capitis and tinea unguium. Griseofulvin morphic fungi commonly found in soil and on plantsbecomes incorporated into the newly synthesized ker- (rose thorns and splinters). Sporotrichosis, the dis-atin layers, inhibiting the growth of fungi. So the skin ease, is an occupational hazard for gardeners. Followingfungi is cleared only after the old keratin has been a prick by a thorn contaminated with Sporothrixreplaced. schenckii, a subcutaneous nodule gradually appears. This nodule becomes necrotic and ulcerates. The ulcer heals, but new nodules pop up nearby and along theCandida albicans lymphatic tracts up the arm. The last type of cutaneous fungal infection is caused Microscopic examination of this fungus reveals yeastby Candida albicans. Candida can infect the mouth cells that reproduce by budding. Culture at 37°C reveals(oral thrush), groin (diaper rash), and the vagina ( Can- yeast, while culture at 25°C reveals branching hyphaedida vaginitis). It can also cause opportunistic systemic (dimorphism). Treat with oral potassium iodide or am-infections. All these infections will be discussed in more photericin B. So if you are going to POT roses you mightdetail later in this chapter (page 150). buy some potassium iodide! SUBCUTANEOUS FUNGAL Phialophora and Cladosporium INFECTIONS ( Chromoblastomycosis) Subcutaneous fungal infections gain entrance to the Fig. 20-3. Visualize a chrome-plated (chromo)body following trauma to the skin. They usually remain fungi blasting cauliflower warts on the skin to helplocalized to the subcutaneous tissue or spread along you remember the disease Chromoblastomycosis. Itl ymphatics to local nodes. These fungi are normal soil is a subcutaneous infection caused by a variety of cop-i nhabitants and are of low virulence. per-colored soil saprophytes (Phialophora and Cla- Figure 20-2 14 6
  • 149. CHAPTER 20. THE FUNGI Figure 20-3dosporium) found on rotting wood. Infection occurs fol- Knowledge of these geographic areas is importantlowing a puncture wound. Initially, a small, violet wart- clinically. For example, Coccidioides has become thelike lesion develops. Over months to years, second most common opportunistic infection in AIDSadditional violet-colored wartlike lesions arise nearby. patients who have resided in Arizona. So a sick AIDSClusters of these lesions resemble cauliflower. Skin patient with a history of previous residence in thescrapings with KOH reveal copper-colored sclerotic Southwest would raise suspicions.bodies. Treat with itraconazole and local excision. Mechanism of Disease All 3 fungi have a similar disease mechanism. Notice the parallels to tuberculosis. SYSTEMIC FUNGAL INFECTIONS Three fungi that cause systemic disease in humans Like Mycobacterium tuberculosis the 3 fungi areare Histoplasma capsulatum, Blastomyces dermati- acquired by inhalation. However, unlike Mycobac-tides, and Coccidioides immitis. All 3 are dimorphic terium tuberculosis, the fungal infections are inhaledfungi. They grow as mycelial forms, with spores, at as a spore form and are never transmitted from per-25°C on Sabourauds agar. At 37°C on blood agar, they son to person. Rather, the spores are aerosolized fromgrow in a yeast form. This dimorphism plays a part in soil, bird droppings, or vegetation. Like Mycobacteriumhuman infection. In their natural habitat (the soil) they tuberculosis, once inhaled, local infection in the lunggrow as mycelia and release spores into the air. These is followed by bloodstream dissemination. In mostspores are inhaled by humans and at the "human tem- infected persons the fungi are destroyed at this pointperature" of 37°C they grow as yeast cells. by the cell-mediated immune system. Antigenic prepa- rations called coccidioidin and histoplasmin areGeography like the PPD of Mycobacterium tuberculosis: when injected intradermally in a previously exposed per-Fig. 20-4. Histoplasma and Blastomyces are en- son they yield a delayed type hypersensitivity reac-demic to the vast areas that drain into the Mississippi tion which results in localized swelling within 24-48River. Visualize a fungi pilot firing a rocket that HITS hours.and BLASTS a hole in the Mississippi River. The 3 fungi have 3 clinical presentations:Fig. 20-5. Coccidioides is endemic to the southwestern 1) Asymptomatic: The majority of cases are asymp-U.S. (Arizona, New Mexico, southern California) and tomatic or mild respiratory illnesses that go unreported.northern Mexico. Visualize Mr. Fungus as he COCKS 2) Pneumonia: A mild pneumonia can develop withhis pistol in the old SOUTHWEST. fever, cough, and chest X-ray infiltrates. Like tubercu- 14 7
  • 150. CHAPTER 20. THE FUNGI Figure 20-4 skin biopsy, etc. The tissue can be examined with silver stain for yeast or can be grown on Sabourauds agar or blood agar. The tissue is the issue!!!! Skin tests are not very helpful for diagnosis, as many people have been previously exposed asymptomatically and will have a positive test anyway. Serologic tests can be helpful (complement fixation, latex agglutination). Acute pulmonary histoplasmosis and coccidioidomy cosis usually require no treatment, as the infection is mild. For chronic or disseminated disease, itraconazole or amphotericin B is often required for months! All Blas. tomyces infections require aggressive amphotericin B or itraconazole treatment. Summary of Histoplasma, Blastomyces, and Coccidioides LIKE TUBERCULOSIS Inhaled, primary in fection in the lung. Asymptomatic, mild, severe, or chronic lung infections. Lung granulomas, calcifications, and/or cavitations.Figure 20-5 1losis, granulomas with calcifications can follow resolu- Can disseminate hematogenouslytion of the pneumonia. to distant sites. A small percentage of persons will develop a severe Skin test like PPD.pneumonia, and an even smaller group will progress toa chronic cavitary pneumonia, marked by weight loss, UNLIKE TUBERCULOSISnight sweats, and low-grade fevers, much like a chronic No person-to-person transmission.tuberculosis pneumonia. Fungi with spores, NOT acid-fast 3) Disseminated: Rarely, the hematogenously bacteria.spread fungi can actually cause disseminated disease,such as meningitis, bone lytic granulomas, skin granu- Fig. 20-6. To remember that Coccidioides, Blasto.lomas that break down into ulcers, and other organ le- myces, and Histoplasma all are inhaled as spores andsions. This disseminated form commonly occurs in the cause disease in the lungs, skin, bones, and meninges,i mmunocompromised host. study Cowboy Fungus. He has spore bullets, cocks All 3 are best diagnosed by obtaining a biopsy of the his gun, then blasts and hits the lung, skin, bone, andaffected tissue: bronchoscopic biopsy of lung lesions, meninges. 148
  • 151. CHAPTER 20. THE FUNGI Figure 20-6Histoplasma capsulatum: This fungus is found in nature, especially in pigeon Nonencapsulated despite its name. droppings. Following inhalation and local lung in- Present in bird and bat droppings, so outbreaks of fection, often asymptomatic, the yeast spreads viapneumonia occur when cleaning chicken coops or the blood to the brain. There is no geographic clus-spelunking (cave exploring). tering of infections as with the other systemic my-Blastomyces dermatitides: coses. Most cases (3/4) occur in immunocompromised persons. In fact, almost 10% of AIDS patients develop Fungi are isolated from soil and rotten wood. cryptococcosis. The rarest systemic fungal infection. A subacute to chronic meningitis develops in crypto- When it does cause infection, it is rarely asympto- coccosis with headache, nausea, confusion, staggeringmatic or mild. Most cases present as chronic dissemi- gait, and/or cranial nerve deficits. Fever and meningis-nated disease with weight loss, night sweats, lung mus can be mild. Cryptococcal meningitis is fatal with-involvement, and skin ulcers. Blastomyces is the hard- out treatment, because cerebral edema progresses toest to get and the hardest to have! eventual brainstem compression. Cryptococcus can also cause pneumonia, skin ulcers, The bLAST to get, and bone lesions like the other systemic fungi. No BLAST to have!!! The key to diagnosis is doing a lumbar puncture andCoccidioides immitis: analyzing the cerebrospinal fluid. An India ink stain Commonly causes a mild pneumonia in normal per- shows yeast cells with a surrounding halo, the polysac-sons in the southwestern U.S. charide capsule. This test is positive half of the time. A Common opportunistic infection in AIDS patients more sensitive test is the cryptococcal antigen test,from that area. which detects cryptococcal polysaccharide antigens. Culture will confirm the diagnosis.Cryptococcus neoformans(Cryptococcosis) Fig. 20-7. AIDS and cryptococcosis. Cryptococcus neoformans is a polysaccharide encap-sulated yeast (not dimorphic) similar to the previous 3fungi in that it is inhaled into the lungs and the in- The usual treatment is with amphotericin B and flucy-fection is usually asymptomatic. It differs in that the tosine. Persons require treatment for as long as 6major manifestation is not pneumonia but rather months with serial lumbar punctures to confirm resolu-meningoencephalitis. tion. AIDS patients may require treatment for life. 14 9
  • 152. CHAPTER 20. THE FUNGI CRYPTOCOCCUS NEOFORMANS YEAST FROM C.S.F. STAINED WITH INDIA INK Figure 20-7Candida albicans cosa and patches of cottage cheese-appearing white( Candidiasis) clumps affixed to the vaginal wall. Imidazole vaginal suppositories are helpful. and in adults between skin folds (under breasts for ex • As a physician you will see this yeast everywhere. It is 3) Diaper rash: Warm moist areas under diapersgiven out like CANDY to humanity: women with vagini-tis, babies with diaper rash, AIDS patients, and the list ample) can become red and macerated secondary togoes on. In the normal host, Candida albicans causes 3 Candida invasion.infections that are cutaneous. In the immunocompro-mised patient, it can cause any of the 3 cutaneous in-fections, as well as cause invasive systemic disease. In Immunocompromised Patients 4) Esophagitis: Extension of thrush into the esoph •In Normal Hosts agus causes burning substernal pain worse with swal lowing. Candida does not infect the esophagus in 5) Disseminated: Candida can invade the blood • 1) Oral thrush: Patches of creamy white exudate immune-competent persons!with a reddish base cover the mucous membranes of themouth. These are difficult to scrape oft with a tongue stream and virtually every organ. When systemic canblade. Swish and spit preparations of nystatin or am- didiasis is suspected, the retina must be examined withphotericin B, or merely sucking on imidazole candies the ophthalmoscope. Multiple white fluffy candidalwill resolve this infection. patches occasionally may be visualized. Clinical 2) Vaginitis: There are 20 million cases of "yeast in- Point: Since Candida is normal flora, it is often culfection" every year in the U. S. alone! Women develop Lured from the urine, sputum, and stool. These can rep-Candida vaginitis more frequently when taking antibi- resent contaminants. However, isolation from the bloodotics, oral contraceptives, or during menses and preg- is never normal and must be respected!!!nancy. The symptoms are vaginal itching and discharge Diagnosis is made with KOH preparation of skin(thick copious secretions wetting the underwear). scrapings, or with stains and cultures of biopsied tissueSpeculum examination reveals inflamed vaginal mu- or blood. 150
  • 153. CHAPTER 20. THE FUNGIFigure 20-8 Systemic infection requires amphotericin B or the Figure 20-9oral antifungal imidazole called fluconazole. THE FUNGI-LIKE BACTERIA:Aspergillus flavus ACTINOMYCETES and NOCARDIA(Aspergillosis) Fig. 20-10. Actinomycetes are bacteria acting like fungi. These are procaryotic organisms and are truly ASPIRATION of ASPERGILLUS = ASTHMA bacteria. They are discussed here because they fre-Fig. 20-8. The spores of Aspergillus mold are floating quently grow in the form of mycelia and are water andin the air everywhere. Some persons develop an soil saprophytes. The 2 that cause human disease areasthma-type reaction to these spores. They have a type1 hypersensitivity reaction (IgE-mediated immediateallergic reaction) with bronchospasm, increase in IgEantibodies, and blood eosinophilia. They also manifest atype 4 reaction (delayed type cell-mediated allergic re-action) with cell-mediated inflammation and lung infil-trates. Systemic corticosteroids are an effectivetreatment.Fig. 20-9. Persons with lung cavitations from tuber,culosis or malignancies can grow an aspergillus fungalball in the cavity, called an aspergilloma. This ball canbe large (as big as a golf ball) and require surgical re-moval. Immunocompromised hosts can develop invasivepneumonias and disseminated disease. Bloody sputummay occur, due to blood vessel wall invasion by As-pergillus hyphae. Aspergillus flavus and other fungi produce toxinsthat cause liver damage and liver cancer. These toxinsare called mycotoxins. The toxin produced by As-pergillus flavus is called the aflatoxin. This has world-wide significance since Aspergillus grows ubiquitously,contaminating peanuts, grains, and rice. The fact thathalf of the cancers south of the Sahara desert in Africaare liver cancers and 40% of screened foods contain afla-toxins suggests that this is a real threat. Figure 20-10 15 1
  • 154. CHAPTER 20. THE FUNGIActinomyces and Nocardia, both of which are gram- only Actinomyces forms sulfer granules and only Nopositive rods. cardia is acid-fast.Actinomyces Israelii Nocardia asteroides There are 4 concepts you should know about this Nocardia forms weakly gram-positive, partiallyorganism: acid-fast beaded branching thin filaments! It is not considered normal flora. Infections with Nocardia are 1) It is a gram-positive, beaded, filamentous anaero- frequently misdiagnosed as tuberculosis because it isbic organism that grows as normal flora in the mouth acid-fast and it causes the same disease process. Likeand GI tract. Mycobacterium tuberculosis, Nocardia is inhaled and 2) It causes eroding abscesses following trauma to grows in the lung to produce lung abscesses and cavita-the mucous membranes of the mouth or GI tract. The in- tions. Erosion into the pleural space can occur, as wellfection is named according to the area of the body as blood-bourne dissemination, resulting in abscesses inthrough which the abscess erodes: cervicofacial the brain and other organs. Immunocompromised pa-actinomycosis, abdominal actinomycosis, and tho- tients, especially those taking steroids, are particularlyracic actinomycosis. at risk for Nocardia infection. Treatment is with 3) When examined under the microscope, the pus trimethoprim and sulfamethoxazole.draining from the abscess reveals yellow granules, Treatment of Actinomyces and Nocardia is a SNAP!called sulfur granules. These are not composed of S ulfa forsulfur but of microcolonies of Actinomyces and cellular Nocardiadebris. Actinomyces give 4) Treatment of this gram-positive bacterium is with Penicillinpenicillin G and surgical drainage. Note: Actinomyces and Nocardia are both filamen- Fig. 20-11. Summary of the fungi.tors, beaded, branching gram-positive organisms, but 152
  • 155. Figure 20-11 FUNGI
  • 156. Figure 20-11 (continued) M. Gladwin and B. Trattler, Clinical Microbiology Made Ridiculously Simple C~MedMaster
  • 157. CHAPTER 21. ANTIFUNGAL ANTIBIOTICSThe number of fungal infections has risen dramatically Adverse Effectswith the increase in patients who are immunocompro-mised from AIDS, chemotherapeutic drugs, and organ On the wards this drug is referred to as am-transplant immunosuppressive drugs. For this reason photerrible and Awfu ltericin because of its nu-you will frequently use the handful of antifungal an- merous adverse effects:tibiotics available. 1) Renal toxicity: (Poor Mr. Kidney!) There is a Ergosterol is a vital part of the cell membranes of dose-dependent azotemia (increase in BUN and creati-fungi but is not found in the cell membranes of humans, nine reflecting kidney damage) in most patients takingwhich contain cholesterol. Most antifungal agents bind this drug. This is reversible if the drug is stopped. Themore avidly to ergosterol than to cholesterol, thus more creatinine level must be followed closely, and if it be-selectively damaging fungal cells than human cells. By comes too high (creatinine > 3), the dosage may have tobinding to or inhibiting ergosterol synthesis, they in- be lowered, terminated, or switched to alternate daycrease the permeability of the cell membranes, causing regimens.cell lysis. 2) Acute febrile reaction: A shaking chill (rigors) We can divide antifungal agents into 3 groups: with fever occurs in some people after IV infusion. This 1) Antifungal agents that are used for serious sys- is a common side effect.temic infections: 3) Anemia. Amphotericin B, the grandfather of antifungal 4) Inflammation of the vein ( phlebitis) at the IV site. agents. This drug covers almost all medically impor- These side effects are important because they are tant fungi but must be given intravenously (not ab- very common. In fact, when amphotericin B is given in sorbed orally) and causes many side effects. It may the hospital, it is usually given with aspirin or aceta- also be given intrathecally (into the cerebrospinal minophen to prevent the febrile reaction. Daily BUN fluid). and creatinine levels are drawn to monitor kidney func- Itraconazole, given orally, has now proven use- tion. You can see that these side effects are important ful for many of these infections. in day-to-day clinical management! 2) Antifungal agents that are used for less serious Fig. 21-1. Properties of amphotericin B, the "am-systemic infections: phibian terrorist": i ntravenous drug delivery; fung- The oral azole drugs. The prototype is keto- icidal by binding to ergosterol in the fungal cell mem- conazole. There are now new agents in this class, brane, causing membrane disruption and osmotic lysis called fluconazole and itraconazole ( mentioned of the cell; nephrotoxicity. above). To speed amphotericins travel through the kidneys 3) Antifungal agents that are used for superficialfungal infections: and decrease renal toxicity, hydration with normal Griseofulvin (taken orally) and the many saline is used commonly with traditional amphotericin B. This hydration is generally not required with the topical antifungal agents such as nystatin newer preparations of amphotericin B. Electrolyte re- and the azole drugs (clotrimazole and miconazole). placement is another important adjunct of ampho- tericin therapy because amphotericin causes increasesAmphotericin B in urinary excretion of potassium, magnesium and bicarbonate. The classic antifungal antibiotic is amphotericin B. New preparations of amphotericin B are now availableMost species of fungi are susceptible to it, and although that add different lipids (fats!) to the traditional (old fash-it has many side effects, it remains the drug of choice for i on) amphotericin B deoxycholate. The addition of themost serious systemic fungal infections: lipid decreases the nephrotoxicity of the drug, making it Systemic Candida i nfections. less Amphoterrible. Cryptococcal meningitis: used in combination with Amphotericin B colloidal dispersion (ABCD:flucytosine. Amphocil): Ampho B + cholesterol sulfate. Rigors still Severe pneumonia and extrapulmonary Blastomyco- occur but nephrotoxicity is reduced.sis, Histoplasmosis, and Coccidioidomycosis. Amphotericin B lipid complex (ABLC): Ampho Invasive Aspergillosis. B + dimyristoylphosphatidylglycerols and dimyris- Invasive Sporotrichosis. toylphosphatidylcholines. Rigors still occur but there is Mucormycosis less nephrotoxicity. 15,5
  • 158. CHAPTER 21. ANTIFUNGAL ANTIBIOTICSFigure 21-1 Liposomal amphotericin B (Ambisome): A unil- wrestling partner of amphotericin B. Amphotericin Bamellar liposome containing a mixture of 1 molecule of busts holes in the cell membranes and flucytosine en-amphotericin B surrounded by a coating of nine mole- ters and inhibits DNA/RNA synthesis.cules of lipid (soy lecithin, cholesterol, and dis- Most fungi are resistant to flucytosine, but Crypto-tearoylphosphatidylglycerol), like a coated jaw breaker. coccus and Candida are the exceptions. Flucytosine useThere is little nephrotoxicity or rigors. is mostly limited to the treatment of cryptococcal Some hospitals make their own concoction by adding meningitis, in conjunction with Amphotericin B.amphotericin B deoxycholate to Intralipid (parenteralfat for intravenous feeding) in a mixture of 1-2 mg am-photericin B per ml lipid. Less nephotoxicity is seen, but Adverse Effectsonce again we do not yet know enough about antifun-gal efficacy. 1) Bone marrow depression, resulting in leukope- nia and thrombocytopenia. Remember that most an- timetabolite type drugs will do this (methotrexate, sulfaFlucytosine drugs, 5-fluorouracil, etc.). 2) Nausea, vomiting, diarrhea. This again is com- Flucytosine is rarely used alone because of rapid de- mon with the antimetabolites, such as the chemothera-velopment of resistance. Think of it as the tag team peutic drugs. 156
  • 159. I CHAPTER 21. ANTIFUNGAL ANTIBIOTICS The reason for these adverse effects is that the drugs Fluconazole damage DNA during its formation in rapidly dividing cells such as bone marrow and GI epithelial cells. Fluconazole is one of the triazoles; it is less toxic and has broader antifungal coverage than ketoconazole. Like ketoconazole it is used for cutaneous Candida in- The Azole Family fections but it is also used as a second-line agent behind amphotericin B for systemic candidiasis and cryptococ- The azole family may be classified into 2 groups of cal meningitis. In AIDS patients who have had crypto- drugs: the imidazoles and the triazoles. coccal meningitis, maintenance with fluconazole will prevent relapses. IMIDAZOLES TRIAZOLES The big picture with fluconazole is that it kills Can- Ketoconazole Fluconazole dida albicans very well: Miconazole Itraconazole 1) Studies comparing it to amphotericin B in the Clotrimazole Voriconazole treatment of systemic Candida albicans infection (in non-neutropenic patients) demonstrated equivalent The azoles inhibit the cytochrome P-450 enzyme sys- effcancy. tem, which is involved in ergosterol synthesis. The de- 2) A single dose of fluconazole very effectively clears pletion of ergosterol disrupts the permeability of the candida vaginitis. fungal cell membrane. These drugs are active against a broad spectrum of fungi. Clotrimazole and miconazole are too toxic for sys- Itraconazole temic use and for this reason, are primarily used for This triazole is becoming the next amphotericin B but topical fungal infections, including pityriasis versi- in an oral formulation without the many amphoterrible color, cutaneous candidiasis, and the dermatophytosis side effects!!! (tinea pedis, corporis, etc.). Clotrimazole troches (like Itraconazole is now used as first-line treatment candies) are sucked to treat oral Candida (thrush), and for chromoblastomycosis, histoplasmosis, coccidioido- clotri mazole vaginal suppositories treat Candida mycosis, blastomycosis, and possibly for invasive vaginitis. aspergillosis. The main problem with this drug is Ketoconazole, fluconazole, and itraconazole are poor oral absorption. Taking it with acid drinks tolerated orally and have many important uses for sys- such as orange juice or colas enhances absorption temic fungal infections. ( need low pH). A new IV formulation has also been de- veloped to avoid poor absorption. Ketoconazole Ketoconazole, one of the imidazoles, is the drug of Voriconazole choice for chronic mucocutaneous candidiasis ( Can- dida on every surface). It is NOT used for systemic Voriconazole has a Voracious appetite for fungi!!! candidiasis (amphotericin B, remember?). Ketocona- Voriconazole is a promising triazole antifungal. Al- zole is currently not used for the treatment of systemic though more clinical experience is needed, data are suf- fungal infections. The safer, more efficacious, oral itra- ficient to support its future use in patients with invasive conazole and old faithful, amphotericin B, are the first aspergillosis who have failed to respond to agents of line drugs. choice (i.e. conventional or liposomal amphotericin B, itraconazole). Adverse Effects 1) GI: Nausea, vomiting, and anorexia, all common. 2) Hepatotoxicity: This is usually seen as a tempo- Other Antifungal Drugs rary rise of hepatic enzymes but on rare occasions can lead tohepatic necrosis. Follow enzymes when on this drug. Nystatin 3) Inhibition of testosterone synthesis: Keto- conazole inhibits the cytochrome P-450 system, which is Nystatin, like amphotericin B, binds to ergosterol, in- important in testosterone synthesis. The result is gy- creasing the permeability of the cell membrane and necomastia, impotence, decreased sex drive (libido), and causing cell lysis. decreased sperm production. Think "Nasty Nystatin" because this drug is too 4) Adrenal suppression. toxic to take parenterally (intravenously). It is only 15 7
  • 160. CHAPTER 21. ANTIFUNGAL ANTIBIOTICS Figure 21-2used topically on the skin and mucous membranes. GriseofulvinAlso, since it is not absorbed from the gastrointestinaltract, oral nystatin can be used to treat oral and Fig. 21-3. Visualize griseofulvin as a greasy ful •esophageal infections with yeast or fungi. You will or- cram used to lever the dermatophyte plaques off theder nystatin on the wards as Nystatin, Swish and skin. It inhibits fungal growth by disrupting spindle for •Swallow for treatment of oral, esophageal, and gas- mation, thus preventing mitosis. Note the worker peel •tric candidiasis. It is also given topically for vaginal ing fungus off your "toe,"sis.candidiasis. Griseofulvin deposits in keratin precursor cells inFig. 21-2. Nasty Nystatin cruises down the esopha- the skin, hair, and nails, where it inhibits the growthgus killing fungi on the wall of the esophagus. In one of fungi in those cells. Note that it does not kill the cidal). The uninfected drug-infiltrated keratin precur • fungi; it just inhibits their growth (static rather thanend and out the other! 158
  • 161. CHAPTER 21. ANTIFUNGAL ANTIBIOTICSsor cells mature and move outward toward the kera- synthesis by inhibiting the formation of squalene epox-tinized layer. As the older, infected cells fall off with ide from squalene. Terbinafine tends to accumulatenormal cell turnover, this translates into a slow cure i n nails, and is therefore useful for tinea unguiumof skin fungus. (onychomycosis). It also appears useful in the treat- Adverse effects of griseofulvin are uncommon. They ment of tinea pedis, tinea capitis, and tinea corporis.include headache, nausea, vomiting, photosensitivity, Since it is not metabolized by the cytochrome p450 sys-and mental confusion, in addition to bone marrow sup- tem (as do the azole antifungals), there is little poten-pression (leukopenia and neutropenia). tial for drug-drug interactions.Potassium Iodide Reference Potassium iodide is used to treat sporotrichosis. Re- Bennett JE. Antifungal Agents. In: Mandell GL. Bennett JE,member that you get sporotrichosis from pricking your Dolin R, eds. Principles and Practice of Infectious Diseases.finger in the garden. "You get Sporotrichosis while Pot- 4th edition. New York: Churchill Livingstone 1995;ting plants." If the infection becomes systemic, ampho- 401-410.tericin B or itraconazole is better. Jackson CA, et al. Drug therapy: Oral azole drugs as systemic antifungal therapy. N Engl J Med 1994;330:263-272.Fig. 21-4. Summary of the anti-fungal drugs. Sanford JP, Gilbert DN, et al. Guide to antimicrobial therapy 1994. Antimicrobial Therapy, m c, Dallas Texas; 1994.Terbinafine Terbinafine is a new oral fungicidal agent that Recommended Review Articles:blocks fungal cell wall synthesis. It blocks ergosterol Terrell CL. Antifungal agents. Mayo Clin Proc 1999:74:78-100. Figure 21-3 159
  • 162. Figure 21-4 ANTI-FUNGAL DRUGS M. Gladwin and B. Trattler. Clinical Microbiology Made Ridiculously Simple WedMester
  • 163. PART 3. VIRUSES Chapter 22. VIRAL REPLICATION and TAXONOMY Viruses have these unique characteristics: 1) They are energy-less. They float around until they come in contact with an appropriate cell. 2) They are basic life forms composed of a protein coat, called a capsid, that surrounds genetic material. Viruses do not have organelles or ribosomes. Certain viruses are further enclosed by an external lipid bilayer membrane that surrounds the capsid and may contain glycoproteins. Some viruses also carry some structural proteins and enzymes inside their capsid. 3) The genetic material is either DNA or RNA. Never both!! The genetic material contains instruc- tions to make millions of clones of the original virus. 4) Replication of the genetic material occurs when the virus takes control of the host cells synthetic ma- chinery. Viruses contain all of the genetic information, but not the enzymes, needed to build millions of replicas of the original virus. VIRAL MORPHOLOGY They say we learn best by doing, so lets study viral structure by making a virus, starting from the nucleic acid inside and proceeding to the capsid and envelope. Nucleic Acid Fig. 22-2. Viruses are classified as either DNA or RNA viruses. So we have two choices for our virus: DNA or RNA. Of course nothing is quite that simple. The nu- cleic acid strands can be single-stranded, double- stranded, linear, or looped, in separate segments or one continuous strand. The nucleic acid sequences can en-Figure 22-1 code a simple message or encode hundreds of enzymes and structural proteins.Fig. 22-1. Imagine that a virus is a specially designedmilitary spaceship with a super-resistant outer shell.However, the engineers forgot to build a fuel tank for RNA Virusestheir spaceship. It must therefore drift around until it Let us choose RNA for the core of our virus. There areencounters a satisfactory planet. When it lands, it 3 types of RNA for our virus: positive (+) stranded, neg-transfers the military cargo off the ship. This cargo is ative (-) stranded, or the RNA of the retroviruses.designed to take control of all factories and then instruct The POSITIVE (+) means that the RNA is JUSTthe factories to begin building copies of the original LIKE a messenger RNA (mRNA). When a positive (+)spacecraft (without fuel tanks). When the replica ships stranded RNA virus enters a host cell, its RNA can im-have been constructed, they will depart in mass, leaving mediately be translated by the hosts ribosomes intothe planet in complete ruins. protein. 161
  • 164. CHAPTER 22. VIRAL REPLICATION AND TAXONOMY pendent RNA polymerase, so negative (-) stranded viruses must carry their own. Fig. 22-3. Translation of positive (+) and negative (-) RNA viruses. One special RNA virus deserves mention here: Retroviruses, of which the HN virus is a member. Fig. 22-4. The RNA of the retroviruses is transcribed in a reverse fashion ("retrograde") into DNA! To do this, these viruses carry a unique enzyme called reverse transcriptase. DNA Viruses Fig. 22-5. Unlike RNA, DNA cannot be translated di- rectly into proteins. It must first be transcribed into mRNA, with subsequent translation of the mRNA intoFigure 22-2 structural proteins and enzymes. Every DNA virus has both a negative (-) strand and When negative (-) stranded RNA viruses enter a cell, a positive (+) strand. Here is the confusing part: Thethey are not able to begin translation immediately. positive (+) strand refers to the strand that is read,They must first be transcribed into a positive (+) strand while the negative (-) strand is ignored.of RNA (like mRNA). To do this, negative (-) strandedRNA viruses must carry, in their capsid, an enzyme Fig. 22-6. Unlike positive (+) stranded RNA, which iscalled RNA-dependent RNA polymerase, which will translated directly into proteins, the positive (+)carry out the transcription of the negative (-) strand stranded DNA is used as a template for transcriptioninto positive (+). Human cells do not have an RNA-de- into mRNA.Figure 22-4 162
  • 165. CHAPTER 22. VIRAL REPLICATION AND TAXONOMYFigure 22-5 Figure 22-6Capsids Now that we know about the different types of nucleicacids, lets build a structure to house the genome. Firstwe will build a capsid. There are two types of capsids:Icosahedral and helical.Icosahedral Symmetry Capsids Figure 22-8Figure 22-7Fig. 22-7. Take 1 or more polypeptide chains andorganize them into a globular protein subunit. This willbe the building block of our structure and is called acapsomer.Fig. 22-5. Arrange the capsomers into an equilateraltriangle.Fig. 22-9. Place 20 triangles together to form anicosahedron. Package the DNA or RNA inside the icosahedralcapsid! Figure 22-9 163
  • 166. CHAPTER 22. VIRAL REPLICATION AND TAXONOMY Figure 22-10Helical Symmetry CapsidsFig. 22-10. In helical symmetry the protein cap-somers are bound to RNA (always RNA because onlyRNA viruses have helical symmetry) and coiled into ahelical nucleoprotein capsid. Most of these assume aspherical shape except for the rhabdoviruses (rabiesvirus), which have a bullet-shaped capsid.EnvelopeFig. 22-11. Now that we have made an icosahedralcapsid with a nucleic acid (RNA or DNA) inside and acoiled helical nucleocapsid (RNA), let us cover the struc-ture with a lipid bilayer membrane. Viruses acquire thismembrane by budding through the host cell nuclear orcytoplasmic membrane and tearing off a piece of themembrane as they leave There may be various glyco-proteins embedded in their cell membranes. Viruses that do not have membranes are referred toas naked or nonenveloped. Those with membranes arereferred to as enveloped. Figure 22-11Finished ProductFig. 22-12. The appearance of the complete viruses 2) Capsid: Icosahedraland their approximate sizes compared to the bacteriumE. coli, and the very small bacteria, Chlamydia, Rick- Helicalettsia, and Mycoplasma pneumoniae. 3) Envelope: CLASSIFICATION Naked Enveloped Viruses are classified according to their: 4) Size: 1) Nucleic acid: The diameter of the helical capsid viruses Type of nucleic acid: DNA, RNA The number of capsomers in icosahedral capsids Double- vs. single-stranded Single or segmented pieces of nucleic acid Positive (+) or negative (-) stranded RNA We will now go over the virus families and the char- Complexity of genome acteristics that separate them. 164
  • 168. CHAPTER 22. VIRAL REPLICATION AND TAXONOMYDNA Viruses 3) Five have icosahedral symmetry: Reo, Picorn Toga, Flavi, Calici (Rhabdo has helical symmetry but These are sometimes referred to as the HHAPPPy shaped like a bullet).viruses: 4) Two undergo replication in the nucleus: Retro Herpes Orthomyxo. Hepadna Adeno Fig. 22-14. The RNA viruses. Papova VIRAL REPLICATION Parvo Pox Most DNA viruses are double-stranded, show icosa- Viruses cannot reproduce on their own. They must in-hedral symmetry, and replicate in the nucleus (where vade a cell, take over the cells internal machinery andDNA customarily replicates). instruct the machinery to build enzymes and new viral Two DNA viruses break these rules: structural proteins. Then they copy the viral genetic material enough times so that a copy can be placed in 1) Parvoviridae: This virus is so simple that it only each newly constructed virus. Finally, they leave thehas a single strand of DNA. It is as simple as playing a host cell. The invading virus also blocks the synthesis ofONE PAR hole in golf. any host DNA, RNA or proteins. This feature forces the 2) Poxviridae: This virus is at the opposite end of host cell to construct only viral proteins and copies ofthe spectrum and is extremely complex. Although it the viral genetic material.does have double-stranded DNA, the DNA is complex in In order for viruses to reproduce, they must completenature, coding for hundreds of proteins. This virus does these 4 steps:not have icosahedral symmetry. The DNA is sur-rounded by complex structural proteins looking much 1) Adsorption and a box ( POX IN A BOX). This virus replicates in the 2) Uncoating of the virus.cytoplasm. 3) Synthesis and assembly of viral products (as well as inhibition of the host cells own DNA, RNA and pro- Three of the DNA viruses have envelopes: tein synthesis). Herpes Hepadna Pox 4) Release of virions from the host cell (either by ly- Three are naked: A woman must be naked for the sis or budding). Adsorption and PenetrationPAP smear exam. PApova Adeno PArvoFig. 22-13. The DNA viruses. Fig. 22-15. The viral particle finds to the host cell which a viral encoded protein on the capsid or a glyco- membrane. This is usually a specific interaction inRNA Viruses protein embedded in the virion envelope binds to a host There are certain generalities about RNA viruses, cell membrane receptor. Unlike the bacteriophagemost of which are the opposite of DNA viruses. virion (see Chapter 3 on Bacterial Genetics), which in- Most RNA viruses are single-stranded (half are jects its DNA, these viruses are completely internalized,positive [+1 stranded, half negative [-1), enveloped, capsid and nucleic acid. This internalization occurs byshow helical capsid symmetry, and replicate in the endocytosis or by fusion of the virion envelope with thecytoplasm: host cell membrane. Uncoating Toga Orthomyxo Corona Paramyxo Retro Rhabdo Picorna Bunya The nucleic acid is released from the capsid into the Calici Arena nucleus or cytoplasm. Transcription, Translation, Replication Reo Fibo Exceptions: RNA Viruses 1) Reoviridae are double-stranded. 2) Three are nonenveloped: Picorna, Calici, and These viruses usually undergo transcription, transla-Reoviridae. tion, and replication in the cytoplasm. 16 6
  • 170. CHAPTER 22. VIRAL REPLICATION AND TAXONOMYFigure 22-15Fig. 22-16. Positive (+) stranded RNA virus replica- POSITIVE (+)tion. These viruses do not carry an RNA dependent RNA STRANDED RNA VIRUS REPLICATIONpolymerase because they are read by the host directly Figure 22-16as mRNA.Fig. 22-17 Negative (-) stranded RNA virus replica-tion. The virus uncoats, releases a virion associatedRNA polymerase, and must first transcribe the negative( -) strand to a positive (+) strand (using the RNA poly-merase). The positive (+) strand then acts like mRNAand undergoes both transcription and translation.DNA Viruses Transcription and replication usually occur in thenucleus.Fig. 22-18. DNA virus replication. DNA viruses tendto be more genetically complex than RNA viruses. Thus,viral transcription is divided into immediate early,early, and late transcription. Another important con-cept is that DNA viruses act in a similar fashion as ourown genome. Segments of DNA are transcribed in thenucleus into mRNA, are spliced and processed, and themRNA then moves to the cytoplasm (endoplasmic retic-ulum) where translation occurs. Immediate early and Early: The initially tran-scribed mRNA here encodes enzymes and proteinsneeded for DNA replication and for further transcrip- NEGATIVE (- )tion of late mRNA. STRANDED RNA VIRUS REPLICATION Late: The mRNA is usually transcribed after viral Figure 22-17DNA replication has begun and is transcribed from 16 8
  • 171. CHAPTER 22. VIRAL REPLICATION AND TAXONOMYFigure 22-18 DNA VIRUS REPLICATIONprogeny DNA. The capsid structural proteins are syn- Naked virions: The cell may lyse and release thethesized from the late mRNA genome. virions, or the virions may be released by reverse phago- cytosis (exocytosis).Assembly and Release Enveloped virions: The newly formed naked virion acquires its new "clothing" by budding through the The structural proteins and genome (RNA or DNA) Golgi apparatus, nuclear membrane, or cytoplasmicassemble into the intact helical or icosahedral virion. membrane, tearing off a piece of host cell lipid bilayer asThe virion is then released. it exits. 169
  • 172. CHAPTER 22. VIRAL REPLICATION AND TAXONOMY HOST CELL OUTCOME Latent infection: The virus can survive in a sleeping state, surviving but not producing clinically overt infec- Death: With the viral infection, the host cells own tion. Various factors can result in viral reactivation.function shuts down as the cell is commandeered for Chronic slow infection: Some viruses will causevirion replication. This can result in cell death. disease only after many years, often decades, of indolent Transformation: Infection can activate or introduce infection.oncogenes. This results in uncontrolled and uninhibitedcell growth. Fig. 22-19. Summary of virus morphology. 17 0
  • 173. •Note: Deity virus (causes hepatitis) is an incomplete RNA virus. It needs the coinfection with of hepatitis B virus to cause diseaseL O)1 Q VIR Ai . MORPHOLOGY M. Gladwin and B. Trattler, Clinical Microbiology Made Ridiculously Simple ©MedMaster
  • 174. CHAPTER 23. ORTHOMYXOVIRIDAE and PARAMYXOVIRIDAEFigure 23-1 NUCLEOPROTEIN (NP)These 2 viral families have similar structures and theability to adsorb to glycoprotein receptors, particularlyin the upper respiratory tract. The orthomyxoviridaeare all influenza viruses, which cause the "ORdinary SEGMENTED RNAflu." Paramyxoviridae also replicate in the upper respi- Figure 23-2ratory tract and can produce influenza-like illness, butthey also produce a PARAde of distinctly different dis-eases. The paramyxoviridae include parainfluenzavirus, mumps, measles, and respiratory syncytial virus.Fig. 23-1. The orthomyxoviridae and paramyxoviridae. ORTHOMYXOVIRIDAE Understanding the structure of this virus will be im-portant to you as a physician. The ability to produce epi-demics and susceptibility to antibody immunity dvaccination all depend on the viral ultrastructure. Youwill see at the end of this section that the paramyx-oviridae have a similar structure with a few smallchanges (making it oh so easy to learn!).Fig. 23-2. The orthomyxoviridae are spherical virions.At the virion center lie 8 segments of negative ( -) strandedRNA put together with a protein (nucleocapsid protein- NP) into a helical symmetry capsid. Surrounding the nu-cleocapsid lies an outer membrane studded with long 1glycoprotein spikes. There are 2 distinct types of glycopro-tein: one with Hemagglutinin Activity (HA) and onewith Neuraminidase Activity (NA). Anchoring the Figure 23-3bases of each of these spikes on the inside of the viral lipid viral genome into the host cell. So HA is needed for ad•bilayer are membrane proteins ( M-proteins).Hemagglutinin (HA) sorption! Antibodies against HA will block this binding and prevent infection.Fig. 23-3. Hemagglutinin (HA) can attach to hostsialic acid receptors. Sialic acid receptors are present on Neuraminidase (NA)the surface of erythrocytes, so viruses with HA glyco-proteins cause heme-agglutination when mixed with Neuraminic acid is an important component of mucin,red blood cells. the substance covering mucosal epithelial cells and Host cell sialic acid receptors also exist on upper res- forming an integral part of the hosts upper respiratorypiratory tract cell membranes, and HA binding to these defense barrier. As the name implies, neuraminidasereceptors activates fusion of the host cell membrane ( NA) cleaves neuraminic acid and disrupts the mucinwith the virion membrane, resulting in dumping of the barrier, exposing the sialic acid binding sites beneath. 172
  • 175. I CHAPTER 23. ORTHOMYXOVIRIDAE AND PARAMYXOVIRIDAE Fig. 23-4. Viral NA and HA act as tag team wrestling with fever, chills, myalgias, arthralgias, headache, and partners, wrestling down the hosts defenses. NA other miseries? cleaves the cell mucin barrier, while HA fuses to the A: Antigenic Drift: During viral replication muta- cells sialic acid residues, enabling viral adsorption and tions can occur in the HA or NA, leading to changes in penetration. the antigenic nature of these glycoproteins. This is termed antigenic drift because the changes are small, Again, antibodies directed against NA are also just a little drift of the sailboat in the water. The re- protective. sulting new strains are only partially attacked by our i mmune system, resulting in milder disease in adults who have previously acquired antibodies. Major muta- tional changes usually result in altered codon reading Influenza Serology and Epidemiology There are 3 types of influenza virus: A, B, and C. frames and a nonviable virus. These types have many strains separated by antigenic differences in HA and NA. Type A infects humans, other Q: We all think that this is a pesky but mild self-lim- mammals (swine, etc.), and birds. Type B and C have iting disease. It can cause pneumonia and more serious only been isolated from humans. disease in the elderly, but usually it resolves without When looking at the disease influenza, 2 questions complications in 3 to 7 days. So why have there been about epidemiology arise: devastating pandemics of influenza throughout his- tory, as in 1918? Over a few weeks in 1918, 548,452 per- Q: If antibody to the NA and HA are protective, why sons in the U. S., 12.5 million persons in India, and 20do we continually get epidemics of the bothersome flu, million persons worldwide died from this virus.Figure 23-4 173
  • 176. CHAPTER 23. ORTHOMYXOVIRIDAE AND PARAMYXOVIRIDAE A: Antigenic Shift: Now we are really shifting In 1997, a new strain of avian influenza (Influenza A,gears. We are taking the boat mentioned above and H5N1) was transmitted from infected poultry to humansairlifting it to a mountain in the Himalayas. With anti- in Hong Kong. This avian flu virus contained super-genic shift there is a complete change of the HA, NA, charged HA similar to that in the 1918 pandemic thator both. This can only occur with influenza type A killed over 20 million people. The supercharged HA en-because the mechanism involves the trading of RNA abled the virus to kill almost half of the people who becamesegments between animal and human strains. When 2 infected. Fortunately, the virus was poorly transmissiblei nfluenza types co-infect the same cell, undergo replica- to humans, and was controlled by destroying the poultrytion and capsid packaging, RNA segments can be mis- in Hong Kong. This was certainly a close call.packaged into another virus. This virus now wields anew HA or NA glycoprotein that has never been exposed Complications of Influenzato a human immune system anywhere on the planet. Sothe entire human population would be susceptible, lead- Even the normal yearly flu can cause complica- ing to devastating pandemics. tions. The elderly and immunocompromised suffer The new HA and NA antigens are given number sub- more serious illness as the virus spreads to the lower scripts to differentiate them. The pandemic of 1889 respiratory tract, resulting in pneumonia. The viralwas caused by a virus with an H2 hemagglutinin, the infection also lowers the host defenses against pandemic of 1900 was caused by a new virus with H3 many bacteria. Secondary bacterial pneumonias by hemagglutinin; in 1918 a swine flu virus transferred its HA to a human virus and so was called Hswine and others are common and the physician must follow Staphylococcus aureus, Streptococcus pneumoniae, hemagglutinin (HSW). The chart below is only in- patients (especially the elderly) closely until completecluded to demonstrate the many pandemics and their resolution of their illness. New fevers or failure to im- new HA and NA antigenic composition. prove means danger!! Global pandemics: Fig. 23-6. Study the figure of the child with the crown H2N2 (the Rey- Spanish for king) and the lightning bolts 1989: around his head and liver. Children given aspirin when 1900: H3N2 1918: H1N1: "Spanish flu"-highly pathogenic they have influenza or varicella (chicken pox) can de- strain-with high mortality (estimated velop a severe liver and brain disease called Reyes 20-40 million deaths worldwide) Syndrome . It is not yet known why this occurs. Give 1947: H1N1* acetaminophen for fever in children, no aspirin!!!! 1957: H2N2* "Asian flu"-illness but low mortality 1968: H3N2* "Hong Kong flu"-illness but low Diagnostic tests for influenza fall into 4 broad mortality categories: 1977: H1N1* 1. Virus isolation: Culture of the virus allows for genetic and antigenic analysis " Notice also that some strains caused a second pan- 2. Detection of viral proteins: New one hour tests helpdemic as a new unexposed population grows to adulthood. guide the choice of antiviral agentsFig. 23-5. Antigenic drift and shift: For influenza epi- 3. Detection of viral nucleic acid (RNA) in clinicaldemics and pandemics to occur in people other than material is available by reverse transcription fol-children (who do not yet have antibodies), the antigens lowed by PCR (very sensitive method)i n the NA and HA must somehow change, through 4. Serological diagnosis: 4-fold increase in specificantigenic drift and antigenic shift. antibody levels over 2 weeks Figure 23-5 174
  • 177. CHAPTER 23. ORTHOMYXOVIRIDAE AND PARAMYXOVIRIDAE mumps virus, and measles virus. Before reading about each, lets examine the big picture: 1) Think lungs: All adsorb to and replicate in the upper respiratory tract. Respiratory syncytial virus and parainfluenza virus both cause lower respiratory infec- tions (pneumonia) in children and upper respiratory tract infections (bad colds) in adults. 2) Think kids: Most infections occur in children. 3) Think viremia: The viral infection results in dis- semination of virions in the blood to distant sites. Mumps and measles reproduce in the upper respiratory tract and spread hematogenously to distant organs. Mumps can produce local parotid and testes infection (parotitis and orchitis), and measles can produce a se- vere systemic febrile illness. Brain infection (encephali- tis) can occur with both mumps and measles.Figure 23-6 Parainfluenza Virus The parainfluenza virus causes upper respiratory in- fection in adults ranging from cold symptoms such asTreatment and Control rhinitis, pharyngitis, and sinus congestion, to bronchi- Influenza viruses are grown in mass quantities in tis and flu-like illness. Children, elderly, and the im- chick embryos, which are then inactivated, purified, and munocompromised also suffer from lower respiratory used as vaccines. Scientists carefully choose 3 strains tract infections (pneumonia).that are circulating in the population or expected to cause Croup is a parainfluenza infection of the larynx andan outbreak in the next season. These vaccines have vari- other upper respiratory structures (laryngotracheo-able success depending on the accuracy of the "guess- bronchitis) that occurs in children. Swelling of these 1work." The vaccines should be given to the elderly, structures produces airway narrowing. Stridor (ai mmunocompromised patients, and health-care workers. wheezing sound) and a barking cough (like a seal) occur There are now a few choices for treating the flu. as air moves through the narrowed upper airways.Amantadine and rimantidine prevent the uncoatingof influenza A. They can both prevent influenza A Respiratory Syncytial Virus (RSV)infection and can reduce the severity of symptoms.Sanamavir (inhaled) and oseltamivir (oral) are neu- RSV is so-named because it causes respiratory infec-raminidase (NA) inhibitors, which can shorten the tions and contains an F-protein that causes formation ofcourse of influenza A and B. multinucleated giant cells (syncytial cells). This virus differs from the rest of its kin by lacking both the HA and NA glycoproteins. PARAMYXOVIRIDAE RSV is the number one cause of pneumonia in young children, especially in infants less than 6 months of age. The structure of paramyxoviridae is very similar to The virus is highly contagious with outbreaks occurringthat of the orthomyxoviridae. The differences are that: i n winter and spring. The treatment of RSV infection 1) The negative (-) stranded RNA is in a single is less than ideal, with ribavirin studies showing con-strand, not segmented. flicting results. Efforts have therefore focused on pre- 2) HA and NA are a part of the same glycoprotein vention. RSV infection can be prevented in a highspike, not 2 different spikes. percentage of cases with palivizumab, which is a 3) They possess a fusion (F) protein (not present in monoclonal antibody against RSV that is produced by athe orthomyxoviridae) that causes the infected host recombinant DNA method. A blood-derived product,cells to fuse together into multinucleated giant cells serum RSV immune globulin, is also available, but(syncytial cells similar to those caused by herpesviridae comes with the risk of transmission of blood-borneand retroviridae infection). infections. Previously infected persons are not entirely immune, There are 4 paramyxoviridae that cause human dis- but the subsequent infections are usually limited to theease: parainfluenza virus, respiratory syncytial virus, upper respiratory tract. 175
  • 178. CHAPTER 23. ORTHOMYXOVIRIDAE AND PARAMYXOVIRIDAE Mumps Virus Mumps virus replicates in the upper respiratory tract and in regional lymph nodes and spreads via the blood to distant organs. Infection can occur in many organs, but the most frequently involved is the parotid gland. Fig. 23-7. About 3 weeks after initial exposure to mumps virus the parotid gland swells and becomes painful. The testes are also frequently infected. About 25% of infected males who have reached puberty can de velop orchitis. The testes enlarge and stretch the cap- sule, resulting in intense pain. Infertility is a rare complication. Meningitis and encephalitis can also oc- cur, the former being more common and less severe. There is only one antigenic type, and a live attenu- ated viral vaccine is a part of the trivalent measles- mumps-rubella (MMR) vaccine. Measles Virus Due to the effectiveness of the MMR vaccine, there were only 2,900 cases of measles in the U. S. in 1988. However, the disease continues to have worldwide im- pact with about 2 million deaths annually. Fig. 23-8. The clinical manifestations of measles (also Figure 23-7 called rubeola). Exposure Measles virus is highly contagious and spreads through nasopharyngeal secretions by air or byFigure 23-8 176
  • 179. CHAPTER 23. ORTHOMYXOVIRIDAE AND PARAMYXOVIRIDAE Figure 23-9 Figure 23-10direct contact. The virus multiplies in the respira- Kopliks Spotstory mucous membranes and in the conjunctivalmembranes. Incubation lasts for 2 weeks prior to the Fig. 23-10. Kopliks spots. A day or 2 before the rash,development of rash. the patient develops small red-based lesions with blue- white centers in the mouth. Think of a cop licking a red- white-blue lollipop.ProdromeFig. 23-9. Measles prodrome. Prior to the appearance Rashof the rash, the patient suffers from prodromal illnesswith conjunctivitis, swelling of the eyelids, photophobia, The measles rash is red, flat to slightly bumpy (mac-high fevers to 105° F, hacking cough, rhinitis, and ulopapular). It spreads out from the forehead to the face,malaise (feels cruddy). neck, and torso, and hits the feet by the third day. 17 7
  • 180. CHAPTER 23. ORTHOMYXOVIRIDAE AND PARAMYXOVIRIDAEFigure 23-11Fig. 23-11. As the measles rash spreads downward, Subacute sclerosing panencephalitis (SSPE) is athe initial rash on the head and shoulders coalesces. slow form of encephalitis caused by measles virus. ManyThe rash disappears in the same sequence as it devel- years after a measles infection the child or adolescentoped. Visualize a can of measles-brand red paint be- may have slowly progressing central nervous systeming poured over a patients head. The paint is thicker disease, with mental deterioration and incoordination.over the head and shoulders and drips completely off The MMR vaccine, which contains live attenuatedin 6 days. measles virus, is preventative.Complications Fig. 23-12. Summary of the orthomyxoviridae and paramyxoviridae. Like mumps, the measles virus disseminates to manyorgan systems and can damage those sites, causing pneu-monia, eye damage, heart involvement (myocarditis), and Recommended Review Articles:the most feared complication, encephalitis. Encephalitis Cox NJ, Subbarao K Influenza. The Lancet 1999; rare, but 10% of patients who develop this will die. Domachowske J, Rosenberg H. Respiratory Syncytial Virus Infection with measles during pregnancy does not Infection: Immune Response, Immunopathogenesis, andcause birth defects but has been associated with spon- Treatment. Clinical Microbiology Reviews April 10, 1999;taneous abortion and premature delivery. In fact, 298-309.measles in pregnant women results in fetal death in genicity of Influenza Virus. Virology 1999; 258: 1-20. Steinhauer D. Role of Hemagglutinin Cleavage for the Patho-20% of cases. 178
  • 181. M. Gladwin and B. Trattler, Clinical Microbiology Made Ridiculously Simple OMedMasterFigure 23-12 ORTHOMYXOVIRIDAE AND PARAMYXOVIRIDAE
  • 182. CHAPTER 24. HEPATITIS VIRIDAEViral hepatitis is an infection of the liver hepatocytes by The details of how to determine which virus is caus-viruses. There are 5 known viruses that infect the liver. ing the hepatitis will be discussed with each virus. 2) Chronic viral hepatitis is more difficult to diag- The 5 RNA viruses are: nose because the patient is often asymptomatic with only an enlarged tender liver and mildly elevated liver. 1) Hepatitis A virus (HAV). function enzyme levels. 2) Hepatitis C virus (HCV), which was previouslycalled NON-A NON-B until it was isolated. 3) Hepatitis D virus (HDV). The Pattern of Liver Enzyme Elevation 4) Hepatitis E virus (HEV). Different diseases result in different patterns of liver. 5) Hepatitis G virus. function enzyme elevation. For example, viral hepatitis usually causes the transaminases ALT and AST to ele- There is 1 DNA virus called: vate to very high levels, while GGT, alkaline phos- phatase, and bilirubin are only mildly elevated. As the 1) Hepatitis B virus (HBV) disease progresses, bilirubin levels rise higher. A gall- Hepatitis A and E are both transmitted via the fecal- stone in the bile duct causes the opposite to occur: biliru- ALT and AST. The reason for this is a fellows.oral route, while the rest are transmitted via blood-to- bin, alkaline phosphatase, and GGT rise higher thanblood (parenteral) contact. Just as A and E are at bothends of ABCDE, so they are transmitted by elements of Fig. 24-1. The hepatocytes produce AST and ALT.both ends of the GI tract. A = Anal, E = Enteric, The cells that line the bile canaliculi produce alka-BCD = BlooD . line phosphatase and GGT. The bile canaliculi carry We will now discuss the clinical disease hepatitis and bilirubin.then cover each virus in more detail. Fig. 24-2. With viral hepatitis there is cell necrosis as VIRAL HEPATITIS the virus takes over the cell machinery. The hepatocytes rupture, resulting in the release of AST and ALT. Some Viral hepatitis can be a sudden illness with a mild to pericanalicular cells will also be destroyed. So we willsevere course followed by complete resolution. This is see very high AST and ALT with a little elevation of al-called acute viral hepatitis and can be caused by all kaline phosphatase and GGT. As the infection worsens,of these viruses. Hepatitis can also have a prolonged the liver swells and the canaliculi narrow, resulting incourse of active disease or silent asymptomatic infection a backup of bilirubin into the blood. So with viral he-termed chronic viral hepatitis. The parenterally patitis the ALT and AST are very high, and the biliru-(blood-to-blood) transmitted HBV, HCV, and HDV can bin, alkaline phosphatase, and GGT rise later in thecause chronic hepatitis. course. 1) Acute viral hepatitis has a variable incubation Fig. 24-3. A stone blocking the bile duct would re-period, depending on the virus type. The growth of the sult in:virus first results in systemic symptoms much like the 1) Inability to excrete the bilirubin, resulting in highflu, with fatigue, low-grade fever, muscle/joint aches, blood levels of bilirubin.cough, runny nose, and pharyngitis. One to two weeks 2) The backup results in increased alkaline phos-later the patient may develop jaundice as the level of phatase and GGT synthesis by the canalicular cells.bilirubin, which is normally cleared by the liver, rises. Imagine the backup of pressure popping the cells, re-As the virus grows in the hepatocytes, these liver cells sulting in the release of alkaline phosphatase and GGT necrose (die). The hepatocytes produce enzymes that are (not the true mechanism but a good memory tool).released during cell death. These are the liver-functionenzymes aspartate aminotransferase (AST), alanine So with an obstructive process (stone in bile duct), ASTaminotransferase (ALT), gamma-glutamyl transpepti- and ALT would only be minimally elevated; alkalinedase (GGT), and alkaline phosphatase. Elevated blood phosphatase, GGT, and bilirubin would be very elevated.levels of these liver enzymes help establish the diagno-sis of hepatitis. Hepatitis A Virus (HAV) So about 2 weeks into the illness, the patient is oftenjaundiced, has a painful enlarged liver and high blood HAV has a naked icosahedral capsid with a posi-levels of liver-function enzymes. tive (+) single-stranded RNA nucleic acid. It is in the 180
  • 183. CHAPTER 24. HEPATITIS VIRIDAE Figure 24-1 family Picornaviridae, and as is the case with most of breaks often occur secondary to fecal-to-hand-to-mouth this family it is transmitted by the fecal-to-oral route contact. Examples of this include an infected food han-( HAV = Anus). dler contaminating food after poor hand washing, per- sons ingesting fecally contaminated drinking water, orEpidemiology close person-to-person contact in institutions such as day care centers. There is a 15-40 day incubation period HAVe you washed your hands??? About 25,000 cases (about 1 month) before the patient develops acute he-of hepatitis A infection are reported each year in the patitis as described earlier.U.S., and there are many more infections that are Young children are the most frequently infected, andasymptomatic or unreported. In fact, 40% of Americans they have a milder course than do adults, often withoutliving in urban centers have serologic evidence of prior developing jaundice or even symptoms. At the other endinfection, but only 5% remember the infection. Out- of the spectrum, a small percentage (1-4%), usually 181
  • 184. CHAPTER 24. HEPATITIS VIRIDAE Figure 24-2adults, will develop fulminant (severe) hepatitis. How- lin will prevent or decrease the severity of infection, ifever, death from HAV is very rare (1%). given early during incubation. Pooled immune serum globulin is obtained by ethanol fractionation from theSerology plasma of hundreds of donors. Since anti-HAV IgG is present in about 40% of the population, there will be an- Serologic tests can help establish the diagnosis. The tibody in the pooled immune serum globulin that will in-HAV capsid is antigenic, resulting in the host produc- activate the virus. Once infection is established,tion of anti-HAV IgM and later, the anti-HAV IgG. A pa- treatment is only supportive.tient with active infection will have anti-HAV IgMdetectable in the serum. Anti-HAV IgG indicates old in-fection and no active disease. This antibody lasts indef- Hepatitis B Virus (HBV)initely and is protective, which means that it willprotect against future infection with HAV. You will have an intimate relationship with HBV throughout your career. Why is this? In an infected pa-Fig. 24-4. Hepatitis A infection: A time line of clinical tient, this virus lives in all human body fluids (semen,symptoms and antibody development. urine, saliva, blood, breast milk. .. ). As a physician,Fig. 24-5. Hepatitis A serology. you will come into contact with patients who harbor this virus. Since hospital workers are considered to be an at-Treatment risk group, you will receive immunization against HBV. So you will touch this virus frequently and will actually A new vaccine is available and may be given to peo- harbor antibodies against it.ple at high risk of HAV infection, such as travelers. If aperson has been exposed, pooled immune serum globu- HBV = Big and Bad 182
  • 185. CHAPTER 24. HEPATITIS VIRIDAEFigure 24-3Figure 24-4 183
  • 186. CHAPTER 24. HEPATITIS VIRIDAE Figure 24-5 SEROLOGY OF HEPATITIS A HBV is very different from HAV. It is a Big (42 NM) der electron microscopy. Notice that the Dane particlevirus with an enveloped icosahedral capsid and double- has an envelope and an icosahedral capsid studded withstranded circular DNA. protein spikes. In its core is a double-stranded DNA with associated DNA polymerase enzyme.Fig. 24-6. The intact virus is called the Dane parti-cle ( Big like a Great Dane) and looks like a sphere un- croscopy, you will notice the Dane particle spheres, de • When looking at infected blood with electron mi- Figure 24-6 184
  • 187. CHAPTER 24. HEPATITIS VIRIDAE scribed above, as well as longer filamentous structures. c) Chronic active hepatitis: The patient has an These filamentous structures (as seen under electron acute hepatitis state that continues without the nor- microscopy) are composed of the envelope and some cap- mal recovery (lasts longer than 6-12 months). sid proteins that have disassociated from the intact 4) Co-infection with hepatitis delta virus virion. This part of the virus is called the hepatitis (HDV): See HDV section. B surface antigen (HBsAg) and is of critical impor- tance because antibodies against this component (anti- Liver injury appears to occur from a cell-mediated im- HBsAg) are protective. Having anti-HBsAg means the mune system attack on HBV. Viral antigens on the sur- patient is immune against HBV. face of infected hepatocytes are targets for cytotoxic Removing HBsAg leaves the viral core, which is T-cells. Immune complexes of antibody and HBsAg cancalled hepatitis B core antigen (HBcAg) and is also deposit in tissues and activate the immune system, re-antigenic. However, antibodies against the core (anti- sulting in arthritis, as well as skin and kidney damage.HBcAg) are not protective (do not result in immunity). Patients who have immunosuppressed states, such as During active infection and viral growth, a soluble malnutrition, AIDS, and chronic illness, are more likelycomponent of the core is released. This is called HBeAg. to be asymptomatic carriers because their immune sys-This antigen is a cleavage product of the viral core struc- tem does not attack.tural polypeptide. HBeAg is found dissolved in theserum, and is a marker for active disease and ahighly infectious state. Pregnant mothers with ComplicationsHBeAg in their blood will almost always transmit HBVto their offspring (90% transmission rate), whereas Primary hepatocellular carcinoma is a compli-mothers who have no HBeAg will rarely infect the cation of HBV. With chronic infection the HBV DNAneonate (10% transmission rate). becomes incorporated into the hepatocyte DNA and triggers malignant growth. There is a 200X increase in the risk of developing primary hepatocellular carcinomaEpidemiology in HBV carriers as compared to noncarriers. Infection with HBV can result in permanent liver scar- HBV is present in human body fluids and is transmit- ring and loss of hepatocytes. This is called cirrhosis.ted from blood-to-blood contact. This non-oral transmis-sion is called parenteral transmission. Transmissionfrom an infected patient can occur by needle sharing, ac- Serologycidental medical exposures (needle sticks, blood spray,touching blood with unprotected hands), sexual contact, Serologic tests help establish HBV infection. Theblood transfusions, perinatal transmission, etc. This many antigens and antibodies are simpler than theyvirus is extremely contagious. seem, as follows: 1) HBsAg: The presence of HBsAg always meansPathogenesis there is LIVE virus and infection, either acute, chronic, or carrier. When anti-HBsAg develops, HBsAg disap- Another reason that HBV is a Bad dude is that pears and the patient is protected and immune.unlike hepatitis A, which can only cause an acute a) HBsAg = DISEASE (chronic or acute)hepatitis, HBV can cause acute and chronic hepati- b) Anti-HBsAg = IMMUNE, CURE, NO AC-tis. The following are disease states caused by BIG TIVE DISEASE!!!BAD HBV: 2) HBcAg: Antibodies to HBcAg are not protective but we can use them to understand how long the infec- 1) Acute hepatitis. tion has been ongoing. With acute illness we will see 2) Fulminant hepatitis: Severe acute hepatitis IgM anti-HBcAg. With chronic or resolving infectionwith rapid destruction of the liver. IgG anti-HBcAg will develop. 3) Chronic hepatitis: a) IgM anti-HBcAg = NEW INFECTION a) Asymptomatic carrier: The carrier patient b) IgG anti-HBcAg = OLD INFECTION never develops antibodies against HBsAg (anti- 3) HBeAg: The presence of HBeAg connotes a high HBsAg) and harbors the virus without liver injury. infectivity and active disease. Presence of anti-HBeAg There are an estimated 200 million carriers of HBV suggests lower infectivity. in the world. a) HBeAg = HIGH INFECTIVITY, virus go- b) Chronic-persistent hepatitis: The patient ing wild! has a low-grade "smoldering" hepatitis. b) anti-HBeAg = LOW INFECTIVITY 185
  • 188. CHAPTER 24. HEPATITIS VIRIDAE Figure 24-7Fig. 24-7. Time course of acute HBV infection, withcomplete resolution and immunity. Figure 24-8Fig. 24-8. Time course of chronic HBV infection, withfailure to develop the protective anti-HBsAg antibodies.Treatment vaccine. There is no risk of developing disease from the Prevention and control of hepatitis B involves: vaccine because it contains only the surface envelope and proteins (HBsAg = no DNA or capsid). The HBV vaccine 1) Serologic tests on donor blood to remove HBV- is now given to all infants at birth, 2, 4, and 15 months; itcontaminated blood from the donor pool. is also given as 3 injections to adolescents and high-risk 2) Active immunization: The vaccine is a recombinant adults (health care workers, IV drug users, etc.).vaccine. The gene coding for HBsAg is cloned in yeast and 3) Anti-viral agents for treatment of chronic active orused to produce mass quantities of HBsAg, used as the persistent HBV infection: 18 6
  • 189. CHAPTER 24. HEPATITIS VIRIDAE Figure 24-9Fig. 24-9. Serology of the medical student vaccinatedwith HBV recombinant vaccine. Figure 24-10 SEROLOGY OF HEPATITIS B Fig. 24-10. Hepatitis B serology. a) The anti-HIV drug lamivudine suppresses HBV DNA to undetectable levels, but most patients have relapses when the drug is discontinued. (Dien- stag, 1995). b) Treatment with interferon alpha suppressed HBV DNA and HBeAg in 50% of treated patients and appears to prevent cirrhosis in these respon- ders (Niederau, 1996). New trials of combination therapy with interferon alpha and ribavirin are planned for patients with chronic active hepatitis B or C.Hepatitis Delta Virus (HDV) This RNA virus is transmitted parenterally and Figure 24-11can only replicate with the help of HBV. The deltavirus helical nucleocapsid actually uses HBVs enve-lope, HBsAg. HDV steals the clothes from HBV and canonly cause infection with the HBsAg coat. 1) Co-infection: HBV and HDV both are transmit-Fig. 24-11. Notice the HBV envelope and proteins ted together parenterally (IV drug use, blood transfu-surround the HDV helical nucleocapsid. Next to it is a sions, sexual contact, etc.) and cause an acute hepatitisconceptual figure of the letter D in a big B. similar to that caused by HBV. Antibodies to HBsAg will be protective against both, ending the HBV+ HDV= Big Bad Dude infection. 2) Superinfection: HDV infects a person who has Without Big Bad HBV, HDV is just a dud and is not chronic HBV infection (like the 200 million worldwideinfectious. Infection occurs in 2 ways: HBV carriers). This results in acute hepatitis in a 187
  • 190. CHAPTER 24. HEPATITIS VIRIDAEpatient already chronically infected with HBV. This olution of liver inflammation (about 50% of treated pa-HDV infection is often severe, with a higher incidence of tients will respond).fulminant hepatitis, cirrhosis, and a greater mortality The problem is that treatment with interferon alpha(5-15%). The patient with chronic HBV cannot make makes patients feel like they have the flu, and onlyAnti-HBsAg and so remains chronically infected with 10-25% will have lasting remissions after therapy isboth HBV and HDV. discontinued (Poynard, 1995). Treatment with the anti-viral drug ribavirin only Serology is currently not very helpful for diagnostic temporarily normalized liver enzymes in 1/3 of patientspurposes because IgM and IgG anti-HDV are in the (Di Bisceglie, 1995). Hepatitis E Virus (HEV)serum for only a short period. As there is no treatment,control of HBV infection is currently the only way to pro-tect against HDV. HEV hepatitis is often referred to as non-A hepati- tis because it shares similarities with HAV. HEV is alsoHepatitis C Virus (HCV) transferred by the fecal-oral route, frequently with the consumption of fecally contaminated water during mon- Blood products were first screened for the presence of soon flooding. The E stands for Enteric (fecal-oral). ItisHBV, and the incidence of post-transfusion hepatitis de- endemic to Asia, India, Africa, and Central America. Hepatitis G Virusclined. However, there was still a risk of developing non-A, non-B hepatitis. Recently an etiologic agent has beenidentified and called hepatitis C virus (HCV). Most ofthe cases (about 90%) of non-A, non-B hepatitis are Hepatitis G is an RNA virus in the Flavivirus family.caused by HCV. Blood products are now also screened It is transmissible by transfusion & parenteral routes.for HCV. It has not conclusively shown to cause liver disease. HCV is transmitted parenterally and has been iden- Fig. 24-12. Summary of hepatitis viruses.tified as an enveloped icosahedral RNA virus. It causesacute and chronic hepatitis in a similar manner as HBV. ReferencesIn fact, HCV should be called hepatitis Cirrhosisvirus because half of those infected develop chronic he- Dienstag JL, et al. A preliminary trial of lamivudine forpatitis. A large percentage of these develop chronic ac- chronic hepatitis B infection. N Engl J Med 1995;333:tive hepatitis and eventual cirrhosis. Hepatocellular 1657-61.carcinoma can develop in patients with chronic active Di Bisceglie AM, et al. Ribavirin as therapy for chronic activeHCV infection and cirrhosis. hepatitis C: a randomized, double-blind, placebo-controlled trial. Ann Int Med 1995;123:897-903. Anti-HCV antibodies develop months after exposure Niederau C, et al. Long-term follow-up of HBeAg-positive pa-and are used to screen donor blood products and aid in tients treated with interferon alpha for chronic hepatitis B.the diagnosis of HCV induced hepatitis. N Engl J Med 1996;334:1422-7. Persons who develop chronic active HCV infection Poynard T, Bedossa P, et al. A comparison of three inter-have a high likelihood of developing cirrhosis and liver feron alpha-2b regimens for the long term treatmentfailure. For patients with chronic active HCV, treat- of chronic non-A, non-B hepatitis. N Engl J Med 1995;ment with alpha-interferon can sometimes result in res- 332:1457-62.
  • 191. Figure 24-12 HEPATITIS VIRIDAE M. Gladwin and B. Trattler, Clinical Microbiology Made Ridiculously Simple ©MedMaster
  • 192. CHAPTER 25. RETROVIRIDAE, HIV, and AIDS ONCOGENES What Is Cancer? Normal cells have strict growth control. They divide an exact number of times with exact timing, depending where in the body they are located. When normal cells are grown on a plate of nutrient media, they form a single layer and stop dividing when they touch each other. This is called contact inhibition. Malignant cells lose contact inhibition and pile up in vitro. They become immortal, dividing continuously as long as there is nutrient supply. In the body this uncontrolled growth causes physical damage by local expansion, steals nutrients from other cells, produces abnormallyFigure 25-1 high levels of hormones or other cell products, and can infiltrate areas where other cells grow (such as the bone marrow).The retroviridae are a large group of RNA viruses thatinfect animals and humans. How Do Oncogenes Cause Cancer?Fig. 25-1. There are 3 big concepts unique to the The normal cell has receptor proteins in the cell mem-retroviridae: RETRO, GROW, and BLOW. brane that regulate cell growth. Growth factors (mito. gems) bind to these receptors to regulate growth. 1) Retro: Most RNA viruses (negative- or positive- Examples of these receptors are the insulin receptor,stranded), enter the host cell and act as mRNA or are the Epidermal Growth Factor (EGF) receptor, and thetranscribed into mRNA. The retroviridae are different. Platelet Derived Growth Factor (PDGF) receptor. Mito-They carry with them a unique enzyme called reverse gen stimulation of these receptors causes intracellulartranscriptase. This enzyme is an RNA-dependent phosphorylation of tyrosine. Phosphotyrosine then actsDNA polymerase that converts the viral RNA into as an intracellular growth messenger.DNA. This viral DNA has unique "sticky" ends thatallow it to integrate into the hosts own DNA, as Fig. 25-2. The Rous sarcoma virus oncogene (src), en-do transposons. codes a transmembrane protein that also phosphory- 2) Grow: Retroviruses can cause cancer in the cells lates tyrosine, but at ten times the normal rate!!!they infect. Genes called oncogenes in humans and an- The erb-B oncogene that causes cancer in chickens en-imals can cause the malignant transformation of nor- codes a protein similar to the EGF receptor. Other onco-mal cells into cancer cells. Some retroviruses carry genes encode proteins that are similar to the PDGF andoncogenes in their genome. Inactive oncogenes in ani- insulin receptors!mals and humans are called proto-oncogenes. Theseare genetic time bombs waiting for activation, which Still other oncogenes encode proteins that act atcan occur by carcinogen-induced DNA mutation or by the nuclear level to promote uncontrolled expression ofretrovirus infection. growth genes. 3) Blow: Some retroviridae are cytotoxic to certaincells, blowing them up. The most notable is the humani mmunodeficiency virus (HIV) which destroys the T- Retroviridae and Oncogeneshelper lymphocytes it infects. This ultimately results indevastating immunodeficiency. Because most of the retroviridae isolated to date cause either leukemia or sarcoma in their vertebrate In this chapter we will discuss: 1) oncogenes; 2) the hosts, they are sometimes called leukemia sarcomahuman retroviridae, using HIV as a model for retroviri- viruses. Some retroviruses cause cancer directlydae structure and genetics; and 3) HIV infection and ( acute) by integrating an intact oncogene into the host4) the Acquired Immunodeficiency Syndrome (AIDS) DNA. Others cause cancer indirectly (nonacute) by acti-caused by HIV. vating a host proto-oncogene. 190
  • 193. CHAPTER 25. RETROVIRIDAE, HIV, AND AIDS Figure 25-2Acute Transforming Viruses The oncogene gene sequence is so long that most acute transforming viruses have lost their own RNAFig. 25-3. Some retroviridae, the acute transforming critical for viral replication. These viruses are called de-viruses, carry intact oncogenes within their viral fective acute transforming viruses and require a co-genome, which when integrated into the host DNA infecting virus to cause cancer.cause malignant transformation. This integration is The Rous sarcoma virus is the only known acutefacilitated by the "sticky" ends and an enzyme called transforming virus that is non-defective. It has the fullintegrase. RNA genome needed for replication and also carries an accessory src oncogene. The acute transforming viruses were discovered in 1911 when Peyton Rous injected cell-free filtered mate- rial from a chicken tumor into another chicken. The Non-acute Transforming Viruses chicken subsequently developed tumor. The causative Fig. 25-4. Other retroviridae, the non-acute trans- agent is now known to be a retrovirus called the Rous forming viruses, activate host cell proto-oncogenes by sarcoma virus which possesses within its DNA an in- i ntegrating viral DNA into a key regulatory area. Thesetact oncogene called src. When the Rous sarcoma virus viruses do not carry oncogenes and thus have room forinfects a cell, it reverse transcribes its RNA into DNA. the full genome necessary for viral replication.The DNA is integrated into the hosts genome by inte-grase. Once integrated the src gene is expressed, caus-ing malignant transformation. HUMAN RETROVIRUSESWhere Do Viral Oncogenes Come From? By the mid-1970s, retroviruses had been discovered in many vertebrate species, including apes. The hy- Studies have shown that normal host DNA has se- pothesis that humans may also be infected with retro-quences that are homologous to viral oncogenes but are viruses led to a search that ultimately resulted in thestill inactive (proto-oncogenes). These genes most likely isolation of a retrovirus from the cell lines and blood ofare involved in cell growth regulation. Somehow, during patients with adult T-cell leukemia. This virus is callednormal viral infection and integration, a mistake in human T-cell leukemia virus (HTLV-I).splicing occurs and a virus "captures" a proto-oncogene. HTLV-I has now been linked to a paralytic diseaseThis proto-oncogene ultimately becomes activated in that occurs in the tropics (Caribbean islands) calledthe virus so the virus now carries an oncogene. t ropical spastic paraparesis. HTLV-1 induced 191
  • 194. CHAPTER 25. RETROVIRIDAE, HIV, AND AIDS Figure 25-3leukemia has also been described in the Caribbean Investigators stimulated T-cell culture growth (T -and Japan. cells from patients infected with AIDS) with inter- A second human retrovirus was isolated from T-cells leukin-2 and were able to find RNA and DNA,of patients with a T-cell variant of hairy cell leukemia. suggesting a retroviral etiology. The virus, whichThis is called HTLV-II, but this virus has no known role was subsequently identified, was called the human A second retrovirus, called HIV-2, causes a dis -in producing disease. immunodeficiency virus (lily). In early 1980 a new epidemic was first noted that we ease similar to AIDS in western Africa. It is a dis -now call the Acquired Immunodeficiency Syn- tantly related virus with 40% sequence homology withdrome (AIDS). Several factors suggested that this dis- HIV-1.ease was caused by a retrovirus: A virus that causes an AIDS-like disease in primates, 1) The infectious agent was present in filtered blood simian immunodeficiency virus (SIV), shares a close se- products, such as concentrated factor VIII given to quence homology with HIV-2. patients with hemophilia. This suggested a viral etiol- ogy, as something small would be necessary to pass HN STRUCTURE the filters. 2) There was a delayed onset between exposure (sex-ual or blood products) and the development of disease. The structure of the virion and genome is similar forThis delayed onset had been observed in the other all of these retroviruses. We will focus on HIV, the causeknown retroviral diseases. of the worlds most feared current epidemic. HIV is at 3) Immunodeficiency occurs with other animal retro- the center of intensive research aimed at halting its dev-viruses, such as feline leukemia virus. Even HTLV-I can astating disease, AIDS.cause immunosuppression. 4) AIDS patients have destruction of the T-helper Fig. 25-5. Under the electron microscope, HIV ap-lymphocytes. The known human retroviruses HTLV-I pears as a spherical enveloped virion with a centraland II were both T-cell tropic. cylindrical nucleocapsid. 192
  • 195. CHAPTER 25. RETROVIRIDAE, HIV, AND AIDS Figure 25-4 To examine this structure fully, we will start from the HN Genomei mide and work outward: Fig. 25-6. The HIV genome (simplified). All retro- 1) At the virion core lie 2 identical SS RNA pieces viruses possess, in their RNA genome, two ending long (a dimer). Associated with these are nucleocapsid terminal repeat (LTR) sequences, as well as the gag (NC) proteins bound to the RNA and the 3 essen- gene, pol gene, and env gene. tial retroviral enzymes, protease, reverse transcrip- tase and integrase. 1) LTRs (long terminal repeat sequences) flank 2) Surrounding the RNA dimer lies the capsid shell the whole viral genome and serve 2 important functions. which has icosahedral symmetry. The proteins that con- a) Sticky ends: These are the sequences, recog- stitute this shell are called capsid proteins (CA). The nized by integrase, that are involved in insertion major capsid protein is p24; this can be measured in the into the host DNA. Transposons, mobile genetic ele-serum to detect early HIV infection. ments, have similar flanking DNA pieces. 3) The rest of the virus has the same structure b) Promotor/enhancer function: Once incorpo-described for the influenza virus (see Chapter 23). Pro- rated into the host DNA, proteins bind to the LTRsteins under the envelope are called matrix proteins. that can modify viral DNA transcription.These proteins serve to hold the glycoprotein spikes 2) gag (Group antigen) sequences code for the pro-that traverse the lipid bilayer membrane (envelope). teins inside the envelope: Nucleocapsid (NC), capsid (CA)- The surface glycoproteins are referred to as gp fol- called p24, and matrix (MA) proteins. Thus, gag codes forlowed by a number: gp 120, and gp 41. the virions major structural proteins that are antigenic. 193
  • 196. CHAPTER 25. RETROVIRIDAE, HIV, AND AIDSFigure 25-5( Figure adapted from Fauci-In: Harrisons, 1994; and Haseltine, 1991) 3) pol encodes the vital protease, integrase, and re- 1) tat encodes the viral TrAnsacTivator protein. verse transcriptase enzymes. The only way the retro- This protein binds to the viral genome and activates viridae maintain their current POL position in the race transcription (thus transactivates). This is a potent pro- to cause human disease is with these unique enzymes. moter of viral activity. Protease is a vital HIV enzyme that cleaves gag and pol 2) rev is another promoter that REVS up viral activ- proteins from their larger precursor molecules (post- ity. It achieves this by a unique mechanism: translational modification). The HIV virus has multiple reading frames, produc- Protease deficient HIV virions can not form their vi- ing different mRNAs depending on where splicing oc- ral core and are non-infectious. New drugs have been curs. It can be spliced into many pieces, producing the developed that block the action of the HIV enzyme, pro- regulatory proteins such as tat, rev, nef (and others: uif, tease. Therapy with these protease inhibitors reduces vpr, and upu). Alternatively, it can be spliced only a few HIV levels and increases CD4 T-lymphocyte cell counts. ti mes to produce the major gag, pol, and enu products Similar benefits occur with drugs that inhibit the re- that form the virion. verse transcriptase enzyme. The rev protein binds to the enu gene to decrease 4) env codes for the ENVelope proteins that, once splicing. So it REVS up the reading of gag, pol, and enu glycosylated, form the glycoprotein spikes gp 120 and to produce virions! gp 41. Gp 120 forms the head and gp 41 the stalk. To- 3) nefs function is uncertain, as experiments have gether they are called gp 160 and bind to CD4 recep- demonstrated that it can both positively and negatively tors on T- cells. regulate HIV expression. Recent studies have shown that persons infected Regulatory proteins are encoded by the regulatory with nef deficient HIV-1 do not develop AIDS and do genes: tat, rev, and nef. Three others (uif, vpr, and not suffer T cell destruction. So nef may play a critical vpu) have poorly understood actions in vivo and will not role in HIV pathogenesis, and vaccines that target nef be discussed. may be useful. 194
  • 197. CHAPTER 25. RETROVIRIDAE, HIV, AND AIDSFigure 25-6Genome Heterogeneity of AIDS cases is on the decline in Western Europe, Aus- tralia, and the United States, the CDC estimates that One of the reasons we are having so much trouble 650-900 thousand persons are currently infected withdeveloping a vaccine against HIV is that it possesses HIV in the United States.the ability to change its genome in a critical area. The disease is transmitted in 2 patterns: 1) In theWithin the enu gene, particularly the area encoding the Americas and Europe 90% of cases are among homo-gp 120 glycoprotein, lie hypervariable regions, where sexuals and IV drug users, resulting in more infectedpoint mutations occur. In fact, duplications and dele- men then women. 2) In developing areas, namely sub-tions also occur here, and they occur in multiples of 3 Saharan Africa, spread is heterosexual with equal maleto preserve the codon reading frame! Even the gene and female infection.coding for reverse transcriptase undergoes frequent The HIV virus is spread by the parenteral route,mutations. In fact, it has one of the highest error rates much like hepatitis B virus. This occurs with:( mutation rates) described, leading to HIV strains re-sistant to zidovudine and other reverse transcriptase 1) Sexual activity: Heterosexual and homosexual ac-i nhibitor medications. This heterogeneity protects the tivity is the most common mechanism of transmis-virus from the human immune system and vaccine in- sion of HIV. HIV is present in seminal fluid as wellduced antibodies. as vaginal and cervical secretions. During or following intercourse, the viral particles penetrate tiny ulcera- tions in the vaginal, rectal, penile, or urethral mucosa. HIV INFECTION Women are 20x more likely than men to get HIV withEpidemiology and Transmission vaginal intercourse, likely because of the prolonged ex- posure of the vagina, cervix, and uterus, to seminal As everyone now knows, we are in the midst of a global fluid. Receptive anal intercourse appears to increase thepandemic of HIV infection. It is estimated that 47 million risk of transmission, likely secondary to mucosal traumapersons worldwide have been infected with the HIV virus of the thin rectal wall. Sexually transmitted diseasesand close to 14 million have died. Ninety percent of in- also increase the risk of transmission. Organisms suchfected persons today live in the developing world and most as Treponema pallidum, herpes simplex virus, Chlamy-are in Africa. In fact, it is estimated that in some countries dia trachomatis, and Neisseria gonorrhoeae cause mu-in Sub-Saharan Africa, one-fourth to one-third of all cosal erosions and may even increase the concentrationadults are infected! The HIV epidemic is rapidly spread- of HIV in semen and vaginal fluids. (Inflammation of theing in South and Southeast Asia. While the total number epididymis, urethra, and vaginal mucosa results in an
  • 198. CHAPTER 25. RETROVIRIDAE, HIV, AND AIDSincrease in HIV laden macro-phages and lymphocytes.) with the CD4 molecule for binding of HIV to lympho-Oral sex is much less likely to result in transmission. cytes and macrophages. 2) Blood product transfusion: HIV can be transmitted Patients who fail to produce normal levels of CKR5i n whole blood, concentrated red blood cells, platelets, proteins appear to be resistant to HIV infection, and cer-white blood cells, concentrated clotting factors, and tain lymphocyte derived proteins (RANTES, MIP1-alpha ,plasma. Gamma-globulin has not been associated with and MIP1-Beta) that bind to CKR5 apper to inhibit HIVtransmission. To reduce the risk of transmission via blood infection. This now opens the door to new classes ofproducts, blood donors are screened for self reported risk drugs that block fusin and CKR5! (Feng, 1996; Cohen,factors and serologic markers of HIV infection. The latter 1996; Deng, 1996; Dragic, 1996; Alkhatib, 1996).i ncludes screening for antibodies to HIV-1 and HIV-2 (by The viral RNA is reverse transcribed into DNA in theELISA) and for p24 antigen. This approach has reduced cytoplasm. Double-stranded DNA is formed and trans-the risk of blood product transmission to 1 in 500,000 ported into the nucleus, where integration into the host units transfused. DNA occurs. The integrated DNA may lie latent or may 3) Intravenous drug use with needle sharing: This activate to orchestrate viral replication. There is some has led to growing numbers of infected persons in U.S. evidence that certain infections, such as with tubercu- urban centers. losis, PCP, cytomegalovirus, herpes, Mycoplasma or im- 4) Transplacental viral spread from mother to fe- munizations, will activate T-cells and may promote tus: The rate of transmission is about 30%, and in- viral replication within the T-cells. Stimulation of T- fection occurs transplacentally, during delivery, and cells results in production of proteins that bind to the perinatally. HIV LTR, promoting viral transcription. 5) Note for students and health care providers: The Following viral replication the new capsids form risk of contracting HIV from a stick with a needle, con- around the new RNA dimers. The virion buds through taminated with HIV infected blood, is 3 out of a thousand the host cell membrane, stealing portions of the mem- ( 0.3%). The risk is much lower for accidental body fluid brane to use as an envelope, leaving the T-cell dead. contact with broken skin. There is virtually no risk in touching an HIV infected patient, unless there is contact Immunology and Pathogenesis with blood or body fluid. The risk goes up if the injury is deep, the needle was in a patients artery or vein, or had Following initial infection, HIV can begin replication blood visible on it, or if the patient has a high viral load i mmediately, resulting in rapid progression to AIDS, or (MMWR, 1995). To put the risk of transmission of HIV by there can be a chronic latent course. The former, most needle stick (0.3% transmission risk) into perspective, common pattern occurs in 3 stages starting with initial the risk of transmission of Hepatitis B virus after a nee- i nfection, marked by an acute mononucleosis-like viral dle stick from a patient who is Hepatitis B e antigen pos- illness. This progresses for a variable number of years itive is about 30%, and for Hepatitis C virus is about 3%. ( median 8 but range of less than 1 to greater than 20) of 6) Epidemiologic evidence indicates that the virus disease-free latency. After AIDS develops most patients is NOT spread by mosquito bites or casual contact die within 2 years if they do not receive effective anti- (kissing, sharing food). There is NO evidence that retroviral therapy (Fig. 25-7). saliva, urine, tears, or sweat, can transmit the virus. 1) An acute viral illness like mononucleosis (fever,Cell Infection malaise, lymphadenopathy, pharyngitis, etc.) develops i n 80% about 1 month after initial exposure. There are Once the HIV virion is in the bloodstream, its gp 160 high levels of blood-borne HIV (viremia) at this stage,(composed at gp 120 and gp 41) glycoproteins bind to the and the viruses spread to infect lymph nodes andCD4 receptor on target cells. This CD4 receptor is pres- macrophages. An HIV-specific immune response arises,ent in high concentration on T-helper lymphocytes. resulting in decreased viremia and resolution of theThese cells are actually referred to as CD4+ T-helper above symptoms. However, HIV replication continuescells. Other cells that possess CD4 receptors in lower in lymph nodes and peripheral blood.concentrations and which can become infected are 2) A clinical latency follows for a median of 8 yearsmacrophages, monocytes, and central nervous system during which there are no symptoms of AIDS, althoughdendritic cells. Following HIV binding to the CD4 re- some patients develop a dramatic generalized lym-ceptor, the viral envelope fuses with the infected host phadenopathy (possibly secondary to an aggressive im-cell, allowing capsid entry. mune attack against HIV harbored in the lymph nodes). Part of the mystery of how HIV binds to the CD4 re- This is not a true viral latency without viral replication;ceptor is as follows. There are two cell surface proteins, HIV continues to replicate in the lymphoid tissue andfusin and CKR5, that are produced by T-lymphocytes there is a steady gradual destruction of CD4 T-lym-and macrophages, respectively. They serve as co-factors phocytes (helper) cells. CD4+ T-helper cells are the 19 6
  • 199. CHAPTER 25. RETROVIRIDAE, HIV, AND AIDS number one target of HIV. The virus reproduces in 2) CD4+ T-cell count of 400-200 (about 7 years): these cells and destroys them. Constitutional symptoms (weight loss, fever, night Toward the end of the 8 years, patients are more sus- sweats, adenopathy) develop as well as annoying skin ceptible to bacterial and skin infections, and can de- infections, such as severe athletes foot, oral thrushvelop constitutional (systemic) symptoms such as fever, (Candida albicans), and herpes zoster. Bacterial infec-weight loss, night sweats, and adenopathy. tions, especially Mycobacterium tuberculosis, become 3) AIDS develops for a median of 2 years followed by more common as CD4 counts drop below 400!!death. AIDS is now defined as having a CD4 T-lympho- 3) CD4+ T-cell count less than 200 (about 8 years):cyte count of less than 200 (with serologic evidence As the immune system fails, the serious opportunisticof HIV infection such as a positive ELISA or west- killers set in, such as Pneumocystis carinii pneumonia,ern blot test) and/or one of many AIDS-defining oppor- Cryptococcus neoformans, and Toxoplasma gondii.tunistic infections, which are infections that usually only 4) CD4+ T-cell count less than 50: At this level thepatients with AIDS develop. These include Candida immune system is almost completely down. Mycobac-esophagitis, Pneumocystis carinii pneumonia, the malig- terium avium-intracellulare, normally only causing in-nancy Kaposis sarcoma, and many others. fection in birds, causes disseminated disease in the AIDS patients. Cytomegalovirus infections also rise asFig. 25.7. The clinical course of HIV infection the count moves from 50 to zero.(acute viral illness, clinical latency, and AIDS) as CD4+T-cells decline over time, and the opportunistic infec- Viral Loadtions that develop at specific CD4 T-cell counts. CD4 counts are used to determine severity of HIV in- 1) Normal CD4+ T-cell counts are 1000 cells/µl blood. fection, risk of opportunistic infection, prognosis, and re-In HIV-infected persons the count declines by about 60 sponse to anti-viral therapy. We can now measure plasmacells/ml blood/year. HIV RNA by the polymerase chain reaction (PCR) or
  • 200. CHAPTER 25. RETROVIRIDAE, HIV, AND AIDSbranched chain DNA assay. There is mounting evidence phocytes, and other immune system effectors. A severethat higher plasma HIV RNA levels (viral load) correlate immunodeficiency state follows the loss of CD4+ T-cells.with a greater risk of opportunistic infection, progression Multinucleated giant cells: This T-cell to T-cell fu-to AIDS, and risk of death (Mellors,1996; Galetto-Lacour, sion allows the virus to pass from an infected cell to an1996). CD4 counts are still the best predictor of a patients uninfected cell without contacting the blood. Thiscurrent risk for particular opportunistic infections. David may protect the virus from circulating antibodies.Ho has popularized the train analogy to explain the pre- B-Lymphocytes: HIV does not actually infect the B-dictive values of HIV viral load and CD4 counts. Viral load cells; however, B-cell dysfunction does occur with HIVtells you the speed at which the train is heading for the infection. There is a polyclonal activation of B-cells, re-cliff (low CD4, development of opportunistic infections sulting in an outpouring of immunoglobulins. Thisand death) while the CD4 count tells you where the train hypergammaglobulinemia results in immune-com-currently is! For example, if a patient has a CD4 count of plex formation and autoantibody production. The most450 cells/mL and a viral load of >10 6 copies/µL that pa- important dysfunction that occurs is a diminished abil-tient is at low risk for developing Pneumocystis carinii ity to produce antibodies in response to new antigens orpneumonia today (CD4>200 cells/micL ) but is at great risk immunization. This is very serious in infants with AIDSin the future for rapid CD4 count decline, opportunistic in- because they cannot develop humoral immunity to thefection and death if not treated. vast number of new antigens they are exposed to. Monocytes and macrophages: HIV infects theseMechanism of T-Cell Death cells and actively divides within them. However, these cells are not destroyed by HIV. This is clinically signifi- The CD4 receptor appears to be involved in T-cell cant in 2 ways:death. Monocytes and macrophages, which possesslower CD4 receptor concentrations, are not destroyed as 1) Monocytes and macrophages serve as reservoirsextensively as are T-cells. for HIV as it replicates, protected within these cells When a T-helper cell is infected, and the virus produces from the immune system.its structural proteins, gp 160 (composed of gp 120 and gp 2) These cells migrate across the blood-brain barrier,41) is integrated into the T-helper cell cytoplasmic mem- carrying HIV to the central nervous system. HIV causesbrane. The virion will bud at the site of gp 160 insertion, brain disease, and the predominant cell type harboringstealing this portion of the membrane to form its envelope. HIV in the central nervous system is the monocyte- Three mechanisms ofT-cell death have been observed: macrophage line. 1) When the virion is budding, the gp 160 (in the T- BIG PICTURE: HN infection diminishes CD4cell membrane) may bind to adjacent CD4 receptors on T-lymphocyte (helper) cell numbers and function.the same T-helper cell membrane, tearing the T-cell The CD4 T-helper cells are involved in all immunemembrane and destroying the cell. responses. So all immune cells have some kind of 2) A second phenomenon occurs between infected altered function. As T-cell numbers decline, thecells and noninfected CD4 cells. The gp 160 in the in- host becomes susceptible to unusual infectionsfected cells binds to other CD4 T-helper cells, resulting and malignancies that normally are easily con-in cell-to-cell fusion. One infected cell can fuse with as trolled by an intact immune system.many as 500 uninfected CD4+ T-helper cells, formingmultinucleated giant cells. ACQUIRED IMMUNODEFICIENCY 3) Gp 160 in the T-cell membrane may mark the cell SYNDROME (AIDS)as non-self, resulting in autoimmune T-cell destructionby cytotoxic CD8 T lymphocytes. Fig. 25-8. The acquired immunodeficiency syndrome (AIDS) is an extremely complex disease. To better un- HIV probably also kills T-cells directly by inhibiting derstand this complexity, consider 2 processes that oc-host cell protein synthesis. cur. The HIV virus causes 1) direct viral disease and 2) disease secondary to the immunodeficiency state.What Is the Clinical Significanceof These Events? 1) Direct viral disease Constitutional (widespread body) symptoms T-Cell death: A healthy person has about 1000 Neurologic damageCD4+ T-helper cells per milliliter of blood. HIV-induced 2) Disease secondary to the immunodeficiency stateT-cell death results in a decline of about 60 CD4+ T- Failure of the immune surveillance system thatcells/µl a year. The T-helper cell plays a vital role in the prevents malignanciesorchestration of the cell-mediated immune system, acti- Secondary infections by pathogens and normalvating and recruiting macrophages, neutrophils, B-lym- flora (opportunistic infections) 198
  • 201. CHAPTER 25. RETROVIRIDAE, HIV, AND AIDSFigure 25-8Constitutional Illness gressive decline in cognitive function referred to as the AIDS dementia complex. Meningeal infection results in AIDS patients suffer from night sweats, fevers, en- aseptic meningitis. The spinal cord can become infected,larged lymph nodes, and severe weight loss. The weight resulting in myelopathy, and peripheral nerve involve-l oss is often referred to as the wasting syndrome. ment results in a neuropathy.Neurologic Disease Malignancies The HIV virus is carried to the central nervous sys- AIDS patients suffer from a high incidence of B-cell tem by the monocyte-macrophage cells. It is unclear at lymphoma, often presenting as a brain mass. Half ofthis time whether the neuronal damage is caused by the B-cell lymphomas in AIDS patients are found to containi nhibition of neuronal growth by the HIV envelope Epstein-Barr virus DNA.proteins or an autoimmune damage caused by the in- Another common AIDS associated malignancy isfected monocyte-macrophages themselves. Kaposis sarcoma. Most cases of Kaposis sarcoma Many patients with HIV infection suffer from some (96%) occur in homosexual men, which suggests thatform of neurological dysfunction. The brain can suffer there may be a co-factor, which appears to be a newdiffuse damage (encephalopathy) resulting in a pro- herpes virus called HHV-8. HHV-8 DNA sequences 199
  • 202. CHAPTER 25. RETROVIRIDAE, HIV, AND AIDS have been found in Kaposis sarcoma, and antibodies of AIDS patients with cryptococcal meningitis will pre- to HHV-8 are found in high concentrations in most pa- sent with headache, mental status changes, or tients (80%) with Kaposis sarcoma and in 35% of ho- meningeal signs. For example: A normal host with mosexual HIV positive men (Moore, 1995; Kedes, meningitis would have meningeal inflammation with 1996; Gao, 1996). The lesions are red to purple, meningismus (positive Kernigs and Brudzinskis sign, plaques or nodules, and arise on the skin all over the stiff neck, headache). An AIDS patient can have a rag-body. The course can range from nonaggressive dis- i ng meningitis with only fever. You must have a highease, with limited spread and only skin involvement, level of suspicion and always consider doing a lumbarto an aggressive process involving skin, lymph nodes, puncture, for cerebrospinal fluid testing, on AIDS pa-l ungs, and GI tract. tients with fever. (More on page 149). Histoplasma capsulatum and Coccidioides im -Opportunistic Infections mitis: These fungi produce disseminated disease in AIDS patients, infecting meninges, lungs, skin, and The most common manifestation of AIDS is the sec- other areas. (More on page 147).ondary infection by opportunists. These are bugs thatare normally pushovers to the intact immune system Viral Infectionsbut wreak havoc in the absence of T-helper defenses (seeFig. 25-7.). Herpes zoster: Painful vesicles develop in der- matomal distribution as the varicella-zoster virus ven-Bacterial Infections tures forth from its latency in the dorsal sensory AIDS patients often have many permanent in- ganglia. AIDS patients can also develop disseminateddwelling intravenous lines or are in the hospital with non-dermatomal zoster.central venous lines. These serve as entry points for bac- Epstein-Barr virus, another herpes family virus, isteremia caused by Staphylococcus aureus or Staphylo- thought to cause oral hairy leukoplakia (OHL). OHLcoccus epidermidis. usually develops when CD4 counts are <400 and is The poorly functioning B-cells and their impaired hu- characterized by white hairlike projections arising frommoral immunity result in more infections with encap- the side of the tongue. This is differentiated from Can-sulated organisms such as Haemophilus influenzae and didal thrush by the fact that OHL will not rub off withStreptococcus pneumoniae. a tongue blade. Herpes simplex: Viral infection results in severe Mycobacterium tuberculosis: Remember the piv- genital and oral outbreaks.otal role of cell-mediated immunity in defense against Cytomegalovirus (CMV): This virus can causeMycobacterium tuberculosis. AIDS patients have a chorioretinitis and blindness. Visual compromise musthigher chance of tuberculosis reactivation (about 10% be looked into carefully in AIDS patients because it canchance per year). (More on page 105). represent the retinal lesions of CMV or brain masses of Mycobacterium avium-intracellulare (MAI): toxoplasmosis and lymphoma. CMV can also causeThis atypical mycobacterium, also called Mycobacterium esophagitis (pain with swallowing) and diarrhea.avium-complex (MAC), can be isolated from many sites(GI tract, liver, bone marrow, lymph nodes, lungs, blood)in infected patients. It causes a smoldering, wasting dis- Protozoal Infectionsease characterized by fever, night sweats, weight loss, Pneumocystis carinii pneumonia (PCP): This isand often diarrhea (GI tract infection) and elevated liver the most common opportunistic infection. Without pro-function tests. (More on page 106). phylactic treatment there is a 15% chance each yearFungal Infections of infection when the CD4+ T-cell count is below 200. AIDS patients who develop PCP have cough and Candida albicans: This yeast is very common in hypoxia. The chest X-ray can be normal or show an in-HIV-infected patients. It causes oral thrush and terstitial infiltrates. Pneumothorax complicates 2% ofesophagitis. Thrush looks like white plaques on the oral PCP cases. About 80% of AIDS patients will get this atmucosa and when scraped off with a tongue blade leaves least once in their lifetime unless prophylactic antibi-a red bleeding base. (More on page 150). otics are taken. (More on page 235). Cryptococcus neoformans: This fungus causes a Toxoplasma gondii: This parasite causes mass le-meningitis in about 10% of AIDS patients. Fever, nau- sions in the brain in 15% of AIDS patients. Patientssea, and vomiting may hint at cryptococcal meningitis. present with fever, headache, and focal neurologicImportant: AIDS patients are similar to the elderly and deficits (seizure, weakness, aphasia). A CT scan willchildren: Without a full immune system they often show contrast-enhancing masses in the brain. (More ondo not exhibit meningeal inflammation. Only 25% page 234). 20 0
  • 203. CHAPTER 25. RETROVIRIDAE, HIV, AND AIDS Cryptosporidium, Microsporidia, and Isospora Prevention belli. These parasites cause chronic diarrhea in patients with AIDS. (More on page 231). Education to avoid high-risk activities (needle sharing, multiple sexual partners, unprotected sex). DIAGNOSIS of HIV and AIDS Screening blood products with ELISA and p24 antigen. Following infection with HIV, viral RNA or antigens (such as p24) can be detected in the blood within weeks. Vaccine Development Three to