Aerobic spore forming bacilli

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Aerobic spore forming bacilli

  1. 1. Aerobic Spore Forming Bacilli <ul><li>Classification </li></ul><ul><li>Most members are saprophytic organisms prevalent in soil, water and air and on vegetation </li></ul><ul><li>Some are insect pathogens </li></ul><ul><li>Genus: bacillus – large aerobic, gram +ve rods in chains </li></ul><ul><li>Species: </li></ul><ul><li>Bacillus anthrax – principal pathogen, a major agent of bioterrorism and biologic warfare, causes anthrax </li></ul><ul><li>Bacillus cereus – cause food poisoning, occasionally eye or other localized infection </li></ul><ul><li>Bacillus subtilis </li></ul><ul><li>B. thuringiensis, B. popilliae, B. sphaericus, B larvae and B. lentimorbus – pathogens for insects, commerc. insecticides </li></ul><ul><ul><ul><ul><ul><li></li></ul></ul></ul></ul></ul>
  2. 2. Bacillus Species <ul><li>Morphology and Identification </li></ul><ul><li>Typical Organisms </li></ul><ul><li>1 x 3-4  m, square ends, in long chains </li></ul><ul><li>B. anthracis has poly-D-glutamic acid capsule </li></ul><ul><li>Spores located in the center of nonmotile bacilli </li></ul><ul><li>Culture </li></ul><ul><li>Colonies of B. anthracis round, a cut glass appearance in transmitted light </li></ul><ul><li>Hemolysis uncommon with B. anthracis </li></ul><ul><li>Gelatin is liquefied, growth in gelatin stabs resembles an inverted fir tree </li></ul>
  3. 3. Bacillus Species
  4. 4. Bacillus Species
  5. 5. Bacillus Species, cont. <ul><li>Growth Characteristics </li></ul><ul><li>Simple sources of nitrogen and carbon for energy and growth </li></ul><ul><li>Spores are </li></ul><ul><ul><li>Resistant to environmental changes </li></ul></ul><ul><ul><li>Withstand dry heat and certain chemical disinfectants for moderate periods </li></ul></ul><ul><ul><li>Persist for years in dry earth </li></ul></ul><ul><li>Animal products contaminated with anthrax spores e.g. hides, bristles, hair, wool, bone can be sterilized only by autoclaving </li></ul>
  6. 6. Bacillus anthracis <ul><li>Pathogenesis </li></ul><ul><li>Anthrax is primarily a disease of herbivores – goats, sheep, cattle, horses </li></ul><ul><ul><li>Rats relatively resistant to infection </li></ul></ul><ul><li>Human infected incidentally by contact with infected animals or their products </li></ul><ul><li>In animals, portal of entry is the mouth and GIT </li></ul><ul><li>Spores from contaminated soil ingested with spiny or irritating vegetation </li></ul><ul><li>In humans, infection acquired by the entry of spores thro </li></ul><ul><ul><li>Injured skin  cutaneous anthrax </li></ul></ul><ul><ul><li>Rarely mucous membranes  gastrointestinal anthrax </li></ul></ul><ul><ul><li>Inhalation of spores into the lung  inhalation anthrax </li></ul></ul>
  7. 7. Bacillus anthracis, cont. <ul><li>Spores germinate in the tissue at the site of entry </li></ul><ul><li>Growth of vegetative organisms  formation of a gelatinous edema and congestion </li></ul><ul><li>Spread via lymphatics to the bloodstream </li></ul><ul><ul><li>Multiply freely in the blood and tissues shortly before and after animal’s death </li></ul></ul><ul><li>That does not produce capsule is not virulent </li></ul><ul><li>Does not induce anthrax in test animals </li></ul><ul><li>Capsule is antiphagocytic, gene on a plasmid </li></ul><ul><li>Anthrax toxin (genes on plasmid) made up of 3 proteins </li></ul><ul><ul><li>Protective antigen (PA) </li></ul></ul><ul><ul><li>Edema factor (EF) and </li></ul></ul><ul><ul><li>Lethal factor (LF) </li></ul></ul>
  8. 8. Bacillus anthracis, cont. <ul><li>PA binds to specific cell receptors, following proteolytic activation it forms a membrane channel that mediates entry of EF and LF into the cell </li></ul><ul><li>EF is an adenylyl cyclase, with PA it forms a toxin known as edema toxin </li></ul><ul><li>LF plus PA form lethal toxin, a major virulence factor and cause of death in infected animals </li></ul><ul><li>Inhalation anthrax (Woolsorter’s disease) </li></ul><ul><li>Spores from the dust of wool, hair or hides are inhaled </li></ul><ul><li>Phagocytosed in the lungs, transported by the lymphatic drainage to mediastinal lymph nodes, germination occurs  toxin production, hemorrhagic mediastinitis, sepsis, fatal </li></ul><ul><li>In anthrax sepsis, # of organisms in blood >10 7 /ml prior to death </li></ul>
  9. 9. Bacillus anthracis, cont. <ul><li>Pathology </li></ul><ul><li>In susceptible animals, proliferate at the site of entry </li></ul><ul><ul><li>Capsule remain intact </li></ul></ul><ul><ul><li>Organisms surrounded by large amount of proteinaceous fluid containing few leukocytes, rapidly disseminate and reach bloodstream </li></ul></ul><ul><li>In resistant animals, proliferate for a few hrs  massive accumulation of leukocytes </li></ul><ul><li>Capsule gradually disintegrate and disappear, remain localized </li></ul><ul><li>Clinical Findings </li></ul><ul><li>In humans,  95% of cases are cutaneous anthrax </li></ul><ul><ul><li>5% inhalational </li></ul></ul><ul><li>GI anthrax very rare, reported from Africa, Asia, USA, following ingestion of meat from infected animals </li></ul><ul><li>Bioterrorism events in the fall 2001 </li></ul><ul><ul><li>22 cases of anthrax; 11 inhalation, 11 cutaneous </li></ul></ul><ul><ul><li>5 of inhalation anthrax died, the rest survived </li></ul></ul>
  10. 10. Bacillus anthracis, cont. <ul><li>Cutaneous anthrax </li></ul><ul><li>Occurs on exposed arms or hands, face and neck </li></ul><ul><li>Pruritic papule develops 1-7 days after entry/spores </li></ul><ul><ul><li>Resembles an insect bite </li></ul></ul><ul><li>Papule  vesicle, coalesce  necrotic ulcer </li></ul><ul><ul><li>Lesions 1-3 cm diameter, central black eschar </li></ul></ul><ul><li>Marked edema occurs </li></ul><ul><li>Lymphangitis, lymphadenopathy, fever, malaise, headache </li></ul><ul><li>After 7-10 days, eschar is fully developed </li></ul><ul><li>It dries, loosens and separates, healing by granulation and leaves a scar </li></ul><ul><li>20% of patients  sepsis, meningitis and death </li></ul>
  11. 11. Bacillus anthracis, cont. <ul><li>Inhalation anthrax </li></ul><ul><li>IP as long as 6 wks </li></ul><ul><li>Marked hemorrhagic necrosis and edema of mediastinum </li></ul><ul><ul><li>Substernal pain may be prominent </li></ul></ul><ul><ul><li>Pronounced mediastinal widening visible on CXR </li></ul></ul><ul><li>Hemorrhagic pleural effusion; cough secondary to effects on trachea </li></ul><ul><li>Sepsis occurs, hematogenous spread to GIT, meninges  bowel ulceration, hemorrhagic meningitis </li></ul><ul><li>Fatality rate is high in the setting of known exposure </li></ul><ul><li>Animals acquire anthrax through ingestion of spores, spread from intestinal tract </li></ul><ul><ul><li>Rare in humans, GI anthrax is extremely uncommon </li></ul></ul>
  12. 12. Bacillus anthracis, cont. <ul><li>Diagnostic Lab Tests </li></ul><ul><li>Specimens </li></ul><ul><li>Fluid or pus from a local lesion, blood, sputum </li></ul><ul><li>Microscopy </li></ul><ul><li>Stained smears from dead animals  large GPR </li></ul><ul><li>In dried smears by immunofluorescence staining techniques </li></ul><ul><li>Culture </li></ul><ul><li>On BA  nonhemolytic gray to white colonies </li></ul><ul><ul><li>Comma-shaped outgrowth (Medusa head) may project </li></ul></ul><ul><li>In semisolid medium, always nonmotile </li></ul><ul><li>B. cereus exhibit motility by swarming </li></ul><ul><li>On bicarbonate-containing medium in 5-7% CO 2  demonstration of capsule </li></ul>
  13. 13. Bacillus anthracis, cont. <ul><li>Lysis by a specific anthrax  -bacteriophage helpful in identification </li></ul><ul><li>Animal inoculation </li></ul><ul><li>Virulent org. kill mice or guinea pigs on intraperitoneal inj. </li></ul><ul><li>Biochemical test </li></ul><ul><li>Carbohydrate fermentation is not useful </li></ul><ul><li>Gelatin liquefaction, index of proteolytic activity </li></ul><ul><li>Serology </li></ul><ul><li>ELISA, not extensively studied </li></ul><ul><li>Acute and convalescent sera in 4 wks apart should be tested </li></ul><ul><ul><li>Positive result is a 4-fold change </li></ul></ul><ul><ul><li>A single titer >1:32 </li></ul></ul>
  14. 14. Bacillus anthracis, cont. <ul><li>Resistance and Immunity </li></ul><ul><li>Active immunity to anthrax induced in susceptible animals by vaccination with </li></ul><ul><ul><li>live attenuated bacilli, spore suspensions or PA from culture filtrates </li></ul></ul><ul><li>Animals graze in known anthrax disease should be immunized for anthrax annually </li></ul><ul><li>Anthrax vaccine available for humans in US </li></ul><ul><ul><li>An aluminium hydroxide-precipitated preparation of PA from sterile filtrate of cultures of avirulent strain </li></ul></ul><ul><ul><li>2 inoculations yielded significant protection from inhalation anthrax in rhesus monkeys </li></ul></ul><ul><li>In Russia, a live attenuated spore-based vaccine widely used in humans in large field trials </li></ul>
  15. 15. Bacillus anthracis, cont. <ul><li>Treatment </li></ul><ul><li>Ciprofloxacin for treatment of anthrax </li></ul><ul><li>Penicillin G, along with gentamicin or streptomycin previously used to treat anthrax </li></ul><ul><li>In the setting of potential exposure </li></ul><ul><ul><li>Prophylaxis with ciprofloxacin or doxycycline should be continued for 4 wks </li></ul></ul><ul><ul><li>While 3 doses of vaccine are being given </li></ul></ul><ul><ul><li>Or for 8 wks if no vaccine is administered </li></ul></ul><ul><li>B. cereus resistant to penicillin </li></ul><ul><ul><li>Doxycycline, erythromycin or ciprofloxacin alternatives to penicillin </li></ul></ul>
  16. 16. Bacillus anthracis, cont. <ul><li>Epidemiology, Prevention and Control </li></ul><ul><li>Soil is contaminated with anthrax spores from carcasses of dead animals </li></ul><ul><ul><li>Remain viable for decades </li></ul></ul><ul><ul><li>Can germinate in soil at pH 6.5 at proper temperature </li></ul></ul><ul><li>Grazing animals infected thro injured mucous membranes serve to perpetuate chain of infection </li></ul><ul><li>Contact with infected animals or their hides, hair and bristles is the source of infection in humans </li></ul><ul><li>Control measures include: </li></ul><ul><li>Disposal of animal carcasses by burning or by deep burial in lime pits </li></ul><ul><li>Decontamination of animal products </li></ul><ul><li>Protective clothing and gloves for handling potentially infected materials </li></ul><ul><li>Active immunization of domestic animals and high occupational risk personnel with live attenuated vaccines </li></ul>
  17. 17. Bacillus cereus <ul><li>Produces toxins that cause disease that is more an intoxication than a food-borne infection </li></ul><ul><li>Food poisoning has two forms: emetic and diarrhoeal </li></ul><ul><li>Emetic type </li></ul><ul><li>Commonly contaminates rice </li></ul><ul><li>When large amount of rice are cooked and allowed to cool slowly, spores germinate and vegetative cells produce toxin during log-growth phase or sporulation </li></ul><ul><li>Begins 1-5 hrs after ingestion of rice and occasionally pasta dishes </li></ul><ul><li>Nausea, vomiting, abdominal cramps, occasionally diarrhoea </li></ul><ul><li>Self-limiting, with recovery within 24 hrs </li></ul>
  18. 18. Bacillus cereus, cont. <ul><li>Diarrhoeal type </li></ul><ul><li>Associated with meat dishes and sauces </li></ul><ul><li>Enterotoxin may be preformed in the food or produced in the intestine </li></ul><ul><li>IP 1-24 hrs </li></ul><ul><li>Profuse diarrhoea with abdominal pain and cramps </li></ul><ul><li>Fever and vomiting uncommon </li></ul><ul><li>Presence of B. cereus in a patient’s stool not sufficient to make a diagnosis </li></ul><ul><ul><li>Bacteria may be present in normal stool specimens </li></ul></ul><ul><ul><li>A concentration of 10 5 bacteria or more/g of food is diagnostic </li></ul></ul>
  19. 19. Bacillus cereus, cont. <ul><li>Important cause of eye infections, severe keratitis, endophthalmitis and panophthalmitis </li></ul><ul><li>Introduced into the eye by foreign bodies assoc. with trauma </li></ul><ul><li>Also assoc with endocarditis, meningitis, osteomyelitis, pneumonia </li></ul><ul><ul><li>Presence of medical device or IVD use predisposes </li></ul></ul><ul><li>Genes from B. thuringiensis coding for insecticidal compounds inserted into genetic material of some commerc. plants </li></ul><ul><ul><li>Assoc with concern on environmental activitists about genetically engineered plants and food products </li></ul></ul>
  20. 20. Bacillus cereus, cont.

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