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GETNET AYALEW(BSc., MSc.)
UoG, CMHS, School of Biomedical
and Lab. Sciences
Department of Medical
Microbiology
4. Systemic bacteriology
Introduction
• The human body is inhabited by thousands of
different bacterial species, some living transiently,
others in a permanent parasitic relationship.
• Likewise, the environment that surrounds us,
including the air we breathe, water we drink, and
food we eat, is inhabited by bacteria, many of which
are relatively avirulent and some of which are
capable of producing life threatening diseases.
• The systemic bacteriology is aimed to
improving your understanding of the
– Important bacterial pathogens
– The disease they cause
– Pathogenesis
– Laboratory diagnosis
– Treatment options
– Prevention and control measures
4.1. Gram positive cocci
STAPHYLOCOCCUS
General characteristics
 Staphylococcus: staphyle, meaning ‘bunch of grapes’
 S. aureus are widely distributed in nature and cause infections of
varying severity; some are members of the normal flora
 There are about 33 spp of Staphylococci
 Species of medical importance:
– S. aureus
– S. epidermidis
– S. saprophyticus
STAPHYLOCOCCI
Staphylococcus aureus
Cultural characters:
• Facultative anaerobes
• Grow on nutrient agar producing golden yellow colonies of
1-2 mm(MSA)
• Produce disease through:-
- ability to multiply & invade tissue
- Production of extracellular enzymes & toxins
• produce β-haemolytic colonies on blood agar.
alpha hemolysis
Beta hemolysis
Antigenic composition
S. aureus cell wall components & antigens:
• Teichoic acid, protein A:
– It binds to Fc portion of IgG, used in co-agglutination.
• Capsule in some strains, make it more virulent surface
receptors for bacteriophages that permit ‘phage typing’ for
epidemiologic purposes
• Coagulase - causes the clumping of non-capsulated strains
when mixed with a solution containing fibrinogen, e.g. plasma.
Enzymes & toxins produced by S. aureus:
1. Coagulase production
– Most definitive virulence factor of S. aureus
2. Cytotoxins: α, β, γ toxins and P-V leukocidin, δ
Haemolysins:
– cause lysis of RBC of many animal spp demonstrated
as β-hemolysis on blood agar.
3. Exfoliative toxin:
– Cause the desquamation seen in SSSS in young
children- produced by phage group II strains
4. Toxic shock syndrome toxin (TSST-1):
– Produced by strains that cause the toxic shock
syndrome (manifest by fever, shock, etc)
5. Enterotoxins:
– Toxins are heat stable and resistant to the
action of gut enzymes
– They cause diarrhoea & vomiting associated
with staphylococcal food poisoning.
6. Other toxins and enzymes include:
– Leukocidin - Staphylokinase
– Proteinase - Lipase
– Catalase - Hyaluronidase
Diseases produced by S. aureus:
A. Focal suppuration(pus) and abscess formation:
1. Superficial infection:
– Folliculitis, carbuncles, boils, stye, mastitis, abscess
formation
2. Deep-seated lesions:
– Osteomyelitis, septic arthritis, endocarditis,
meningitis, endocarditis, bronchopneumonia,
empyemia, etc.
3. Bacteraemia with multiple abscesses in tissues.
– Outbreaks of hospital wound infections commonly
occur due to antibiotic resistant staphylococci.
B. Toxin-mediated staphylococcal diseases
1. Food poisoning
– Results from ingestion of preformed enterotoxin in
contaminated food that is improperly cooked and
kept unrefrigerated for some time.
– Source of contamination of food: the hands or nose
of a cook / food handlers /carriers.
– Types of food involved in staphylococcal food
poisoning are carbohydrate rich foods, e.g. cakes,
pastry, milk, etc.
– IP: short (1-8 hrs) followed by nausea, vomiting,
diarrhoea and general malaise with no fever.
2. Toxic shock syndrome (TSS):
– This is associated with TSST-1, first described in
menstruating women using tampons. The syndrome also
occurs with wound or localized infections.
– TSS has an abrupt onset of fever, vomiting, diarrhoea,
muscle pains, rash Hypotension, heart and renal failure may
occur in severe cases.
3. Staphylococcal scalded skin syndrome (SSSS):
– Occurs due to the exfoliative toxin produced by
phage II strains of S. aureus.
– The syndrome occurs in babies and young children.
– It is characterized by large areas of desquamation
of the skin and generalized bullae formation.
Menstruation-associated TSS
Less than 5% of women carry S. aureus in their vaginal flora
only one in five have the potential to produce TSST-1.
FIGURE . Evidence of staphylococcal scalded-skin syndrome in a 6-year-old
boy. Nikolsky’s sign, with separation of the superficial layer of the outer epidermal
layer, is visible.
Laboratory diagnosis:
Specimens
– Swabs from lesions: pus, sputum, CSF, blood,
urine examined
Gram stain smears: Gram positive cocci in clusters
Culture:
– S. aureus colonies show complete haemolysis on
blood agar and golden yellow
Figure: Gram positive cocci
Coagulase negative staphylococci (CoNS)
S epidermidis
– Inhabitant of the skin.
– It is involved in indwelling catheters, prosthetic
materials, shunts, surgery
– It is a common cause of prosthetic heart valve
endocarditis
– It also causes nosocomial bacteremia
– Often multiple antibiotic resistance - Methicllin
S. saprophyticus
• Commonly isolated from animals and their
carcasses.
• S. saprophyticus is resistant to the antibiotic
Novobiocin, a characteristic used in Lab. to
distinguish it from S. epidermidis
• It is a 2nd most common cause of UTI, after E. coli
in young women accounting for 10-20% .
• It also causes soft tissue infections
STREPTOCOCCUS
• General feature
– Non-motile, non-spore forming, catalase-negative
Gram positive cocci arranged in chains.
– Widely distributed in nature, some are
commensals in the throat, intestine.
– Others cause human diseases
– Others found in water, dust, milk /milk products.
– Most are facultative anaerobes
– More than 30 spp are identified.
• Scanning electron microscope image of Streptococcus
Streptococcus
Classification:
• Heterogenous group of bacteria
I. According to their O2 requirements
– aerobic
– anaerobic
II. according to their action on RBC in blood agar
– Beta haemolytic streptococci: complete
haemolysis (clear zone around the colonies on BA)
e.g. S. pyogenes, S. agalactiae
– Alpha haemolytic streptococci: partial
haemolysis e.g. Viridans streptococci,
S. pneumoniae
– Non-haemolytic or gamma streptococci: no
haemolysis/ change in RBC's, e.g. Enterococci
III. based on serologic reactivity of cell wall
polysaccharide Ags (group c carbohydrate )
• Also known as Lancefield groups
– Group A - S. pyogenes
– Group B - S agalactiae
– Group C - S. equisimilis
– Group D - Enterococci
– Group H - S. Sanguis
– Group K - S. salivarius
Streptococcus pyogenes
• Known as Group A streptococcus (GAS)
• The most important human pathogen causing
diseases including:
– Suppurative conditions / Skin infections
– Throat infections
– Systemic infections
– Non-suppurative sequelae
• About 5-15% of normal individuals harbor the
bacterium, in their respiratory tract, without signs of
disease.
Virulence factors of group A streptococci:
1. M -protein, fibronectin-binding proteins (e.g. F
protein) & lipoteichoic acid for attachment
2. Hyaluronic acid capsule: inhibits phagocytosis
3. Exotoxins such as pyrogenic toxin, cause the rash
of scarlet fever & systemic toxic shock syndrome
4. Invasins - Streptokinase, streptodornase (DNase
B), hyaluronidase & streptolysins
Pathogenesis:
Diseases due to toxins
1. Streptococcal sore throat and follicular tonsillitis
(pharyngitis)
– It is characterized by enlarged tonsils with
purulent exudates, high fever and enlarged
cervical lymph nodes
2. Impetigo: A local infection of the skin characterized
by formation of blisters which break leaving surface
covered with pus or crusts
II. Diseases due to invasion:
• Diffuse rapidly spreading infections that
involve the lymphatics with minimal local
suppuration infection can extend to the blood
stream.
1. Puerperal sepsis:
• Infection of the uterus after delivery or
abortion leading to endometritis and is
associated with bacteremia.
2. Soft tissue sepsis:
• Wound infection, cellulitis, lymphadenitis,
necrotizing fascitis - may be complicated by
streptococcal septicemia.
3. Acute Bacterial Endocarditis:
• The organism reaches the heart valve through the
blood stream as a complication of any of the
primary lesions mentioned before.
III. NONSUPPURATIVE SEQUELAE:
• Post-streptococcal diseases –GN, RF
– May occur 1- 4 weeks following a primary
inadequately treated group A streptococcal
infection of the skin & Respiratory Tract
• Acute glomerulonephritis (AGN):
– The condition is due to Ag-Ab complex deposition
on the glomerular basement membrane (GBM).
– The majority of patients recover completely.
However few may die or pass to chronic GN &
renal failure.
Rheumatic fever (RF):
• The condition is due to Ag-Ab complex deposition
on the heart valves.
• The onset follows 1-4 weeks after throat infection
with group A streptococci.
• The most serious complication of streptococcal
throat infection since it may result in damage of
the heart valves & muscle
Lab diagnosis of streptococcal diseases:
Specimens: Swabs from throat or other lesions, pus, or
blood in case of bacteraemia
method
– Direct smears stained by Gram’s method show
Gram-positive cocci in chains.
– Cultures done on blood agar show colonies
producing complete haemolysis
– Blood cultures: done for bacteremic infections e.g.
bacterial endocarditis & puerperal sepsis.
Streptococcus agalactiae
• Group B streptococci (GBS)
• out 10% - 30% of pregnant women are colonized
with GBS in the genital tract.
• GBS causes life-threatening infections in newborn
infants
• GBS can also cause serious diseases in pregnant
women, the elderly, and adults with other illnesses.
• In newborns, GBS is the most common cause of
sepsis and meningitis and a common cause of
pneumonia.
• GBS disease in newborns usually occurs in the first
week of life.
Diagnosis
• Lab test of blood or spinal fluid.
Treatment
• Newborns and adults are usually treated with
antibiotics given IV
Enterococcus
• 12 spp, some of these are - Enterococcus faecalis, E.
fecium, S. durans, and S. avium
• They are normal inhabitants of the intestine.
• They cause UTI, wound, cholecystitis blood infections,
meningitis, bacteremia (neonates) subacute
endocarditis, prostatitis.
• Enterococci are among the most common causes of
nosocomial infections, esp in ICU
STREPTOCOCCUS PNEUMONIAE /Pneumococcus/
Habitat:
• normal inhabitant of the human upper respiratory
tract (found as commensal)
• The carrier rate of S. pneumoniae in the normal
human nasopharynx is 20-40%.
Morphology:
• Gram-positive, catalase-negative, lancet-shaped
slightly elongated and arranged in pairs and non-
motile
• Are capsulated in animal tissues.
Pathogenesis:
• S. pneumoniae does not produce toxins
• It owes its virulence to the capsule, which enables
the organism to invade the tissues and resist
phagocytosis.
• Predisposition to disease: if the resistance is
lowered, e.g. by viral respiratory infections, excessive
smoking, alcoholism, malnutrition
Diseases caused by S. pneumoniae
• S. pneumoniae is currently the leading cause of
invasive bacterial disease in children and the elderly.
• Causes 80% of lobar pneumonia; conjunctivitis,
paranasal sinusitis, meningitis, acute exacerbation of
chronic bronchitis, septic arthritis, osteomyelitis,
endocarditis, peritonitis, cellulitis, brain abscess.
Laboratory diagnosis of lobar pneumonia:
1. Direct microscopic examination of gram stained
sputum smears will show the prevalent organism
to be pneumococci.
2. Sputum cultured on blood agar.
Treatment
• Pneumococci are sensitive to many
antibiotics.
• Some isolates have recently been reported to be
resistant to penicillin.
Prophylaxis / Prevention:
1. Pneumococcal conjugate vaccine (PCV7)
– for infant immunization children,
2. Polyvalent polysaccharide vaccine (PPV23)
– for adults - are safe and fairly effective.
– The later is recommended for specially
susceptible individuals, e.g. aged (>65 years),
debilitated or bed-ridden patients or after
splenectomy.
4.2. GRAM NEGATIVE COCCI
Genus Neisseria
• Important properties
– The genus Neisseria contains gram-negative cocci
that resemble paired kidney beans.
– There are two important human pathogens:
• Neisseria meningitidis
• Neisseria gonorrhoeae
– Named after a germ physician aleksandre Nissere
– All Neisseriae are oxidase – positive; i.e. they
possess the enzyme cytochrome C.
NEISSERIA GONORRHOEAE (GONOCOCCI)
• They cause gonorrhoea, a STD of humans.
• Gonococci attack mucus membrane of the GUT, eye,
rectum, throat producing acute suppuration that may
lead to tissue invasion followed by inflammation and
fibrosis.
• Gonorrhea is generally limited to superficial mucosal
surfaces lined with columnar epithelium
Antigenic structure & virulence factors:
• Pili
• LoS
• Proteins
• IgA protease
Diseases
1. Gonorrhoea:
– It is a VD transmitted by sexual intercourse.
– It affects both males & females.
– The IP for gonorrhea is 2-8 days after sexual
contact.
a. Males:
– gonorrhoea is usually in the form of acute
anterior urethritis with purulent urethral
discharge and painful urination.
– The organism may also invade the prostate
resulting in prostatitis or extend to the testicles
resulting in orchitis.
• The involvement of testicles,
b. Females:
– gonorrhoea is in the form of cervicitis & urethritis
with major symptoms include mucopurulent
vaginal discharge and mild lower abdominal pain.
– It may extend to the uterine tubes causing
salpingitis, fibrosis & infertility.
– Asymptomatic males & females are major
problem as unrecognized carriers of the disease.
– About 50% of women with cervical infections are
asymptomatic.
• May affect young girls through contaminated towels
or toilet seats causing vulvovaginitis.
• Cervical involvement may extend through the uterus
to the fallopian tubes resulting in salpingitis, or to the
ovaries resulting in ovaritis.
• About 15% of women with uncomplicated cervical
infections may develop PID
• Involvement of fallopian tubes or ovaries may
result in sterility.
2. Ophthalmia neonatorum:
• An infection of the new born acquired from
the birth canal of gonorrhoeal mother.
• It may involve the cornea leading to
blindness.
3. Occasionally, disseminated infections occur.
Diagnosis:
Acute urithritis (male):
• Urethral discharge examined by direct Gram stain
• Presence of G -ve diplococci intra- & extracellularly in
pus cells
Chronic male; acute and chronic female infection: -
• Morning drop or prostatic discharge in chronic male
infection
Cervical discharge in acute and chronic female infections are examined by:
1. Direct Gram stain - usually hard to detect the organism due to the
presence of normal flora or due to low No.
2. Cultures done on chocolate or Thayer-martin media incubated at 37oC in
atm of 5-10% CO2.
Left: Neisseria gonorrhoeae Gram stain of pure culture;
Right: Neisseria gonorrhoeae Gram stain of a pustular exudate.
Treatment
• Due to emergence of penicillin resistant beta-
lactamase producing strains, antibiotics now used are:-
spectinomycin, tetracyclines & chloramphenicol
Prevention:
• Involves the use of condoms & the prompt treatment
of symptomatic patients.
• Neonatal ophthalmia is prevented by use of
tetracycline or erythromycin eye ointment
immediately after birth.
NEISSERIA MENINGITIDIS (MENINGOCOCCI)
• Highly contagious disease, usually occurs in epidemics
• Capsular polysaccharide Ags; according to which the
meningococci are classified into groups.
• The most important groups associated with disease in
man: A, B, C,Y and W-135 strains .
• Epidemics in Africa are mainly due to group A.
NEISSERIA MENINGITIDIS
Properties of polysaccharide Capsule:
• It enhances virulence by its antiphagocytic action.
• It is the Ag that defines the serologic -groups.
• It is the Ag detected in the spinal fluid of patients
with meningitis.
• It is the Ag in the vaccine that induces protective
immunity.
MENINGITIS
• The disease occurs in epidemics among young adults.
• The organism occurs in the nasopharyx of healthy
carriers.
• The carrier rate is 3-30%. During epidemics, the
carrier rate reaches 80%.
• It starts in the nasopharynx where it remain silent or
gives rise to exudative pharyngitis.
• From the nasopharynx the organism may invade the
blood stream (meningococcemia) causing high fever,
haemorrhagic skin rash etc.
• The infection is transmitted by droplets from
cases or carries.
• Hemorrhagic necrosis of Adrenal glands –
Waterhause - Friderichsen syndrome
characterized by high fever, shock, widespread
purpura, disseminated intravascular coagulation
and adrenal insufficiency.
• Severe bacteremia may be fatal due to circulatory
collapse & suprarenal hemorrhage.
• From the blood stream, the organism reaches the
meninges causing meningitis manifested by fever,
severe headache, vomiting and rigidity of the
neck and back muscles.
• It may progress to coma within few hours.
Diagnosis
1. CSF test
• In meningitis, the CSF is turbid due to the large
number of pus cells; 20,000/ul.
a. The CSF is centrifuged and the deposit is examined
microscopically after Gram stain
• The presence of gram negative diplococci
intracellular in pus cells is diagnostic.
b. The deposit is cultured on chocolate agar or Thayer-
Martin medium and incubated at 37oC in 5-10%
CO2.
C. Detection of meningococcal polysaccharide Ag in CSF by co-
agglutination:-
2. Blood Culture may give positive results.
Prophylaxis:
• Rifampicin 600 mg orally twice daily for 2 days can
eradicate the carrier state and serve as
chemoprophylaxis for contacts.
Vaccination:
• Polyvalent vaccine from the capsular polysaccharide
of groups A, C, Y & W-135 strains available
• It is effective in preventing epidemics of meningitis &
reduce the carrier rate.
• The vaccine does not include the Group B
polysaccharide which is poorly immunogenic in
humans.
• Trials are being made to prepare a recombinant
vaccine.
4.3. GRAM POSITIVE RODS
They are grouped into:
1. Spore forming
– Bacillus specius (B. Ceruse, B. anthracis )
– Clostridium species
• C. Tetani
• C. Perfringens
• C. botulinum
• C. Difficile
2. Nonspore forming
– Corinobacterium species
– Listeria species
THE GENUS BACILLUS
Bacillus:
• Aerobic, G+ve, endospore forming bacilli, occur in chain
• Ubiquitous in nature - soil, water and airborne dust.
• Most spp of are harmless saprophytes (anthracoids)
• Two spp - Bacillus anthracis & B. cereus - are important
pathogenic members.
Bacillus anthracis
Pathogenicity:
The virulence of B. anthracis is dependent upon both
presence of the capsule and production of the toxin.
Bacillus anthracis
Anthrax
• Primarily a disease of animals (sheep, cattle, horses) causing
septicemia & death
• Humans accidentally contract the dis by contact with
infected animals or their products.
There are 3 clinical types:
1. Cutaneous anthrax: (95%)
– It occurs in butchers, farmers & veterinarians.
– Organisms enter through small abrasions, multiply
locally producing a malignant pustule
2. Pulmonary anthrax (wool sorter's disease):
– Rare disease, occurs by inhalation of spores.
– It occurs in persons who handle wool or animal hairs.
Bacillus anthracis
3. Intestinal anthrax:
• Very rare; organisms ingested in infected meat with
invasion and ulceration of the GI mucosa.
• From all these sites invasion of the blood stream
may occur giving rise to septicemic anthrax.
Lab diagnosis:
• Samples taken from skin, sputum, stool, blood.
Direct smears:
• Gram stain - demonstrate G +ve rectangular
long bacilli arranged in long chains with clear
zone representing the capsule.
• The polychrome methylene blue stains the
organism blue while the capsule appears pink
Bacillus anthracis
Culture
• Organism grows on simple & enriched media
Animal inoculation
• In mice or guinea pigs, helpful to differentiate
between anthrax & anthracoids.
Serologic tests
• Precipitating and haemagglutinating Abs
demonstrated in sera of man and animals.
Treatment
• The antimicrobial of choice: penicillin
• Tetracycline, erythromycin be used in pts with
allergy to penicillin
Bacillus anthracis
Prevention:
1. Disposal of animal carcases by burning or by deep
burial in lime pits.
2. Autoclaving of animal products.
3. Protective clothing & gloves for handling
potentially infected materials.
4. Active immunization of domestic animals with live -
attenuated vaccines.
5. High risk persons immunized with a non-living
vaccine
B. cereus
Bacillus cereus
• Motile, causes toxin-mediated food poisoning
after consumption of cooked rice with
enterotoxin
• Toxins released by the bacteria lead to vomiting
and diarrhea (symptoms similar to S. aureus food
poisoning)
1. Diarrheal type
– Characterized by diarrhea & abdominal pain occurring 8-16 hrs
after consumption of the contaminated food.
– Associated with a variety of foods including vegetable dishes,
meat, sauces, pastas, desserts, dairy products
B. cereus
2. Emetic disease
– Nausea & vomiting begin 1-5 hrs after the contaminated
food is eaten.
– Boiled rice and held for prolonged periods at ambient
temp, then quick-fried before serving is usual offender
– Dairy products or other foods are occasionally responsible.
– Frequently misdiagnosed as staph food poisoning.
GENUS CLOSTRIDIA
Clostridia:
– Strictly anaerobic, Gram-positive spore forming bacilli
Natural habitat: the intestinal tracts of animals &
humans; the spore are present in the soil.
Pathogenic clostridia:
• Nearly 100 Clostridium spp identified, but only 25 -30
commonly cause human or animal disease.
• Different groups according to the diseases they
produce:
1. C. tetani - cause tetanus
2. C. perfringens - cause gas gangrene, food poisoning
3. C. botulinum - cause food poisoning
4. C. difficile - cause enterocolitis.
CLOSTRIDIUM TETANI
• Found in the intestine of man, animals & in manured soil.
• It causes tetanus in man & animals.
Morphology:
• Gram-positive, long, chain bacilli with round terminal spores
giving the characteristic ‘drum-stick’ appearance.
• They are motile.
Cultural characters:
• Strict anaerobes, grow on nutrient agar on which colonies are
surrounded by a clear zone of haemolysis due to its
tetanolysin toxin.
• The organism grows on Robertson cooked medium.
CLOSTRIDIUM TETANI
Antigenic structure:
• The neurotoxins produced by all toxigenic strains
of C. tetani are serologically identical.
• 10 types of antigenic variation among flagella
identified.
Pathogenicity:
• Human dis caused by tetanospasmin (neurotoxic
exotoxin)
• Toxins are produced by vegetative cells of C.
tetani
• Toxin production appears to be under a control of
plasmid gene.
CLOSTRIDIUM TETANI
a. Tetanospasmin
– Acts upon the CNS; inhibits release of acetyl choline -
thus interfering with muscular transmission
– Toxin binds to ganglioside receptors; blocks release of
inhibitory mediators (eg. glycine) at spinal synapses, lead
to generalized muscular spasm & hyperflexia.
b. Tetanolysin - haemolytic toxin, is of minor importance in the
pathogenesis of tetanus.
– Infection occurs by contamination of wounds with street
dust containing spores.
– At the local site of infection the spores germinate.
TETANUS
• Injury: e.g. nail prick, surgical wound, gun shot
wound, infected umblical stump leading to
tetanus neonatorum.
• Germination of the spores & development of
vegetative organisms that produce toxin are
aided by: necrotic tissue, calcium salts,
associated pyogenic infections
• The disease is characterized by convulsive tonic
contractions of voluntary muscles.
• Spasm in jaw muscles lead to trismus (lock jaw).
TETANUS
Diagnosis:
• Rests on the clinical picture & history of
contaminated wounds.
• Wound exudate are examined microscopically for the
presence of gram-positive bacilli with drum-stick
appearance.
• The exudate is cultured on blood agar & incubated
anaerobically, on Robertson cooked meat medium.
• The organism is identified by its pathogenicity to
laboratory animals.
TETANUS
Treatment:
1. Antitoxin given at once to suspected cases,
without waiting for lab. diagnosis, in order to
neutralize the toxin before it fixes to CNS.
2. Antibiotics: Penicillin is given in big doses to
inhibit the growth of C. tetani & stops
further toxin production. It may also control
associated pyogenic infection.
TETANUS
Prophylaxis
• Tetanus is a totally preventable disease.
Active immunization:
• Alum precipitated tetanus toxoid is given as
‘DPT’ in 3 IM injections at the age of 2,4 & 6
months.
• Booster doses given to military personnel
before / during war, for pregnant women to
guard against labor infection & to provide
maternal immunity for the new born
TETANUS
Passive immunization:
• Antitoxin given to wounded persons, without
previous history of vaccination.
• Antitoxin prophylaxis should be accompanied by
active immunization with tetanus toxoid.
CLOSTRIDIUM PERFRINGENS
Clostridia that produce invasive infections
• C. perfringens - commonest of members of the genus
clostridium associated with gas gangrene.
• Found in the colon of 25-35% of healthy people, under
certain conditions produce serious, life treating
infections
• C. perfringens type A & C produce enterotoxin which
are responsible for food poisoning.
Morphology:
• Gram-positive large bacilli, the only non-motile spp in
the genus, spores are oval, sub-terminal, non
projecting
• Capsules are formed in tissues.
C. perfringens
Toxins or virulence factors
• C. perfringens produce a variety of toxins &
enzymes that result in spreading of infection.
1. α-toxin (lecithinase) - acts on lecithin which is a
component of the cell membrane.
2. Theta toxin has a haemolytic & necrotizing
effect.
3. DNase, hyaluronidase & collagenase
4. Enterotoxin produced by some strains (types A &
C) causes food poisoning following ingestion of
warmed meat dishes.
• Toxin is released in the gut causing diarrhoea
after 6-18 hrs which lasts for 1-2 days.
C. perfringens
Gas gangrene
• Several species of clostridia may cause gas
gangrene, but the commonest is C. perfringens.
Pathogenesis:
• Infection occurs when wounds are contaminated
with soil containing the organism or its spores the
condition occurs in deep lacerated, devitalized
wounds as in car accidents or war wounds.
• The presence of foreign bodies, mixed infection
with aerobic pyogenic bacteria, decreased blood
supply - lowers O2 tension, favours germination
of spores
GAS GANGRENE
• Vegetative cells multiply, ferment sugars producing gas
- distends the tissues and interferes with blood supply
leading to tissue death.
• Necrotising toxin, collagenase & hyaluronidase favour
necrosis and spread of infection.
• Proteolytic clostridia digest dead tissues leading to
change in colour & foul odour of the wound.
• This is accompanied by generalized toxemia, fatal
Diagnosis:
• Primarily on clinical grounds.
• Bacteriological confirmation from wound exudate &
swabs from deeper areas
• Direct smear are stained by gram - large G+ve rods
GAS GANGRENE
Prevention:
• Prevention depends upon adequate cleaning of
contaminated wounds, surgical removal of foreign
bodies & excision of all devitalized tissues.
• Administration of antibiotics specially penicillin.
• Antitoxic sera for passive prophylaxis is unreliable.
• Toxoids not available for active immunization.
CLOSTRIDIUM BOTULINUM
C. botulinum
• Saprophyte in soil frequently present in the intestinal
tract of domestic animals.
Morphology:
• Gram-positive large straight rods, motile, non
capsulate, spores are oval central or sub-terminal.
Pathogenesis:
• C. botulinum causes botulism produced by ingestion of
the neurotoxin in contaminated canned meat or fish.
• C. botulinum does not replicate easily within the body.
• Such foods provide proper anaerobic conditions for
growth & production of exotoxin.
C. botulinum
Typing:
• 8 serotype (A-H) known, each with a serologically
distinct, but pharmacologically similar toxin.
• Human botulism is usually due to types A, B & E.
Cultural characters:
• Strict anaerobe, grows on simple media.
• Wound botulism can occur in rare cases when
devitalized tissue is contaminated with soil.
• Intestinal botulism in infants, known as floppy baby
syndrome, is due to ingestion of spores, followed by
germination & toxin production in the gut.
• The feeding of honey has been implicated as a possible
cause of infant botulism.
C. botulinum
Toxin:
• It is the most potent poison known.
• During growth of C. botulinum & during autolysis of the
bacteria, toxin is liberated into the environment.
• It acts by preventing release of acetyl choline at motor
nerve ending in the parasympathetic system; destroyed
in 2 min at 60-90oC, dependent on type.
BOTULISM
• An intoxication resulting from ingestion of canned food
containing neurotoxin produced by C. botulinum.
• The toxin has affinity to the cranial motor nerves
causing bulbar paralysis
• Death results from respiratory or cardiac failure.
• There is no diarrhoea or vomiting.
C. botulinum
Diagnosis:
• Toxin can be demonstrated in serum from the patient
• The antigenic type of toxin identified by neutralization
with specific antitoxin in mice. Mice die rapidly.
• C. botulinum grown from left over food and tested for
toxin production (rarely done).
• In infant botulism, C. botulinum & toxin can be
demonstrated in stools but not in serum.
• Toxin may be demonstrated by passive
hemagglutination or RIA
Treatment
• Rapid administration of polyvalent antitoxin.
Prevention
• by careful sterilization of food before canning.
CLOSTRIDIUM DIFFICILE
• Present in the gut of up to 3% of healthy adults, 66% of
infants
• C. difficile infection is the most important cause of
hospital-acquired diarrhea.
Antibiotic-associated Enterocolitis
• It is associated with antibiotic-induced pseudo-
membranous colitis which is the severest form of
antibiotic associated diarrhoea,
• Most common antibiotics are ampicillin & clindamycin.
• The antibiotics disturb the balance of bacteria in the
gut, C. difficile multiply rapidly, produce toxins, cause
illness
Corynebacterium
Important properties
– Non-spore forming, non-acid fast gram-positive bacilli
with club – shaped (wider at one end) and are
arranged in palisades or in V-or L-shaped formations.
– Their arrangements may resemble Chinese letters.
– They are aerobic or facultative anaerobic, non-motile
and Catalase positive organisms.
– Although many species of corynebacteria can function
as opportunistic pathogens, the most commonly
associated human pathogen is Corynebacterium
diphtheria
Corynebacterium diphtheriae
Pathogenesis
• Lysogenic beta phages are able to produce the
diphtheria toxin because the phage carries the
toxin gene.
• Major significant virulence factor produced by
C. diphtheriae is the diphtheria toxin, which is
entirely under the genetic control of the beta-
phage. The toxic is an A-B toxin. It has a B or
binding portion and an A or enzymatically active
portion.
Epidemiology
• Humans are the only natural host of C. diphtheriae.
• Aerosol dissemination spreads the organism from person to
person.
• Rarely by direct contact.
• The organism can also infect the skin especially in the tropics
but can occur world wide in persons with poor skin hygiene.
Disease
• Most prominent sign of diphtheria is thick, gray, adherent
pseudo membrane over the tonsils and throat.
• There are three prominent complications.
– Extension of the membrane in to the larynx and trachea,
causing airway obstruction.
– Myocarditis accompanied by arrhythmias and circulatory
collapse.
Laboratory diagnosis
1. Microscopy- Metachromatic granules in bacteria
stained with methylene blue is important
2. Culture- Specimens collected from the
nasopharynx and throat are inoculated on to
– Media developed specifically for this organism (eg.,
Cyateine –tellurite agar, serum Tellurite agar, Loffler’s
medium).
3. Serology-Toxins A and B can be identified in
faeces by a latex bead agglutination test.
Treatment
• The treatment of choice is antitoxin; it should
be given immediately to neutralize unbound
toxin in the blood. Penicillin G or erythromycin
is recommended also but neither is a
substitute for antitoxin.
Prevention
• Symptomatic diphtheria can be prevented by
actively immunizing people with diphtheria
toxoid during child hood and booster dose
given every 10 years through out life.
Listeria
• Important properties
– The genus Listeria is a small gram positive, non-
spore forming facultative anaerobic bacilli.
– The genus consists of seven species, with Listeria
monocytogenes the only human pathogens.
Listeria monocytogenes
• Listeria preferentially grows intracellular, and
cell mediated immunity is a more important
host defense than hummoral immunity.
• It is distributed world wide and found in plants,
soil and in many domestic animals from which it
may be found in their milk and on their flesh.
• Transmission is associated with consumption of
contaminated food products such as poorly
cooked meats and unpasteurized milk and
cheese.
Disease
• Infection during pregnancy can cause abortion,
premature delivery or sepsis during the
peripartum period.
• Meningitis or sepsis can occur in
immunocompromised adult.
• Gastroenteritis caused by consumption of
contaminated dairy products & under cooked
meats is the major health problem.
Laboratory diagnosis
• Gram-positive rods, small, motile gray colonies with a
narrow zone of beta -hemolysis on blood agar plate
suggest the presence of Listeria.
• Identification of the organism as L. monocytogens is
made by sugar fermentation tests.
Treatment
• Invasive disease can be treated by ampicillin with or
without gentamicin.
• Trimethoprim-sulfamethoxazole is an alternative drug.
Prevention and control
• Limiting the exposure of immunocompressed
patients to potential sources such as infected
animals and their products and contaminated
vegetable is recommended.
• There is no vaccine available to date.
4.4. Gram negative rods
Natural habitat
– the intestinal tract of humans & animals
– Gram-negative, facultative anaerobic bacilli
– About 32 genera, contains >130 spp
– Some genera (e.g. Escherichia, Shigella, Salmonella,
Enterobacter, Klebsiella, Serratia, Proteus, etc).
– Some enteric pathogens, e.g. E. coli, are part of the normal
flora & incidentally cause disease,
– Others: Salmonella & Shigella are regularly pathogenic for
humans.
Morphology:
– Gram-negative bacilli, non-motile or motile by peritrichous
flagella; non-sporing, some encapsulated.
Escherichia coli
• Normal inhabitants of the intestine of man &
animals.
• Some cause disease in humans.
Morphology
• Gram-negative bacilli, motile, some strains are
capsulated.
Cultural characters
• Facultative anaerobes, grow on simple media,
• On MacConkey medium, they produce rose-pink
colonies due to Lactose Fermentation .
Virulence factors:
• Many strains of E. coli have powerful toxins
responsible for disease.
• Pili (adhesive factors)
Diseases caused by Escherichia coli :-
1. UTI:
– E. coli is the commonest cause of UTI.
– Uropathogenic E. coli colonize the vagina &
periurethral region from where they ascend to
the bladder or kidney causing cystitis or
pyelonephritis.
2. Intestinal diseases:
– Different strains of E. coli can cause diarrhoea
through different mechanisms:
a. Enterotoxigenic E. coli (ETEC):
- Certain serotypes, e.g. 06,078 cause traveller's
and infantile diarrhoea.
- The diarrhoea is watery & ranges from mild to
severe cholera - like and may be fatal.
– The organism adheres to intestinal epithelium
through the pili or colonization factors. Then
they liberate enterotoxins.
– The toxin cause diarrhoea by stimulating guanyl
cyclase in intestinal mucosal cells.
b. Enteropathogenic E. coli (EPEC):-
–Certain serotypes e.g. O55, O111 cause
outbreaks of neonatal diarrhoea in
nurseries.
–They act mainly by adhering tightly to
intestinal mucosa resulting in loss of
microvilli & cupping of cells around the
bacteria.
– Thus preventing the normal functions of
absorption & secretion.
c. Enteroinvasive E. coli (EIEC):
– Certain serotypes e.g. O124, O164 cause
dysentery - like diarrhoea through invasion of
intestinal epithelial cells.
d. Enterohaemorrhagic E. coli (EHEC):-
– Certain serotypes e.g. O157. These strains
produce verocytotoxin (VT).
– These strains cause haemorrhagic colitis which is
severe form of diarrhoea with bloody discharge.
Produce shiga toxin
3. Neonatal meningitis: E. coli causes 40% of neonatal
meningitis followed by group B streptococci.
4. It causes bacteraemia & endotoxic shock in
immunocompromised host.
5. It causes hospital-acquired infections
Diagnosis:
• Specimen according to the site of infection e.g. urine,
pus, stools, CSF etc.
• Pathologic material is inoculated on MacConkey
media; LF colonies are further identified by their
morphology & biochemical reactions.
ENTEROBACTER
• Occurrs as indigenous intestinal flora.
• It is similar to klebsiella in many biochemical characters;
however, it is motile.
Species
• E. aerogenes - has small capsules
• Found in intestine or free
• Causes UTI and sepsis
CITROBACTER
• Similar to E. coli except in being citrate positive.
• It antigenically resembles the salmonellae.
• It is seen as opportunistic pathogen in immunocompromised
individuals
• Causes UTI, sepsis, wound infection, osteomyelitis &
gastroenteritis in elderly hospitalized patients.
• Cases of neonatal meningitis also have been reported.
• Spp: C. freundii, C. koseri
KLEBSIELLA
• Normal inhabitants of the intestine & upper
respiratory tract.
• Are saprophytes in soil & water, some cause disease
in man.
Morphology:
• Gram-negative bacilli, non motile and capsulated.
Cultural characters:
• They ferment glucose, lactose, with production of
acid & gas.
Diseases caused by Klebsiella
1. K. pneumoniae
– causes lobar pneumonia.
– It cause hospital-acquired infections, eg UTI.
2. K. rhinoscleromatis causes rhinoscleroma which is a
granulomatous lesion (chronic granuloma) of the
nose & throat /oropharynx.
3. K. ozane: rhinitis
4. K. oxytoca: cause UTI, RTI, wound sepsis
PROTEUS
• Are normal inhabitants of the intestine of man.
• They cause infections only when they leave the intestine.
The important members are:
• Proteus mirabilis: cause UTI
• Proteus vulgaris: nosocomial infections
Morphology:
• Gram-negative bacilli very pleomorphic (variable in
length) and highly motile.
Cultural characters:
• They grow on nutrient agar producing a spreading growth
"swarming". Proteus forms colourless colonies on
MacConkey agar
Biochemical activities:
• They are urease positive (i.e. decompose urea rapidly
• ferment glucose with production of acid & gas,
• produce H2S
Disease
Proteus mirabilis is the most frequently isolated spp.
1. UTI: Urinary urea is "split" by the bacterial urease to
produce ammonium salts: this results in alkaline urinary
pH & an increased risk of urinary calculi.
2. Often isolated from mixed flora of wounds, burns,
pressure sores, chronic discharging ears.
3. Septicaemia.
Treatment:
• Proteus are highly resistant to antibiotics & antibiotic
• Sensitivity tests should be done before treatment.
• P. mirabilis is inhibited by penicillin
• Other members: aminoglycosides & cephalosporins
SALMONELLAE
• The natural habitat is animal gut.
• Predominantly, animal pathogens which can also
cause disease in man.
• Food stuffs from animal sources are important
vehicles in the transmission of infection.
• There are 2 species and more than 2500 serotypes
within the genus salmonella, 4 of them; S. typhi, S.
paratyphi A, B and C cause enteric fever in man.
• Other species cause salmonella food poisoning or
enterocolitis e.g. S. typhimurium and S. enteritidis.
SALMONELLAE
Antigenic structure:
• They posses O (somatic) and H (flagellar) Ags.
Pathogenesis & Diseases caused by salmonellae:
• They cause a variety of conditions, referred as
salmonellosis.
1. Enteric fever
2. Enterocolitis
3. Bacteraemia and septicaemia.
Typhoid fever (Enteric fever )
• Produced by S. typhi, S. paratyphi A, B & C.
• Source of infection is stool or urine of cases or carriers.
• Infecting dose is about 105 organisms
• The organism enters the body by the oral route in
contaminated food or drinks, e.g. raw vegetables,
fruits, raw shell fish & milk products.
• After ingestion, the organism multiplies in payer's
patches,
• passes through the lymphatics to the blood stream
causing bacteraemia that persist for one week.
• It then disseminates to the kidney & is excreted in
urine, & to the liver & is excreted in bile to reach the
intestine.
Clinical features:
• IP 10 -14 days
• fever, malaise, headache, constipation & myalgia with
enlargement of the liver & spleen.
• The fever is a gradually rising (in a step ladder fashion).
• After recovery some individuals continue to harbour
salmonella in their tissues as convalescent or chronic
carriers.
• They carry the organism in the gall bladder or urinary
tract & intermittently excrete it in the stools /urine.
• Such individuals should not work as food handlers.
Diagnosis of enteric fever:
1. Isolation of the organism from blood, urine & stools
2. Detection of Abs in the serum of the patient.
3. Serological diagnosis(widal test )- used to identify
antibody in patients
Prevention
1. Sanitary measures must be taken to prevent
contamination of food and water.
2. Carriers must not be allowed to work as food
handlers.
Treatment:
• The drugs of choice are chloramphenicol, ampicillin
& trimethoprim-sulfamethoxazole.
II. Salmonella Enterocolitis
• Many members of salmonella are responsible for this
condition.
• The most important are S. typhimurium & S. enteritidis.
• These organisms are common pathogens of animals or birds.
Transmission:
• The organism is transmitted from improperly cooked meat of
infected animals, eggs of infected birds or from food
contaminated with rat excreta.
Symptoms:
• The disease is characterized by nausea, vomiting,
abdominal discomfort, diarrhoea & slight fever.
• The condition occurs after multiplication of the
organism in the intestine, i.e. it is an infection and
not due to a toxin.
• The incubation period is 12-18 hrs to allow for such
multiplication.
• Recovery follows within 1week.
III. Septicaemia
• Salmonella septicaemia is characterized by prolonged
fever & anaemia.
• Following oral infection, there is early invasion of the
blood stream with possible focal lesions in the form
of osteomyelitis, pneumonia, meningitis or
endocarditis.
Shigellae
• The natural habitat limited to the intestinal tracts of
humans & other primates, where they cause
bacillary dysentery.
• They are closely related to E. coli.
• Non-motile & non-capsulated.
• They produce pale non-lactose fermenting colonies
on MacConkey media.
Antigenic structure:
• According to the somatic O Ags shigellae are
divided into 4 serogroups or species and
numerous serotypes:-
- S. dysentriae - 13 serotypes
- S. boydii - 18 serotypes
- S. flexneri - 6 serotypes
- S. sonnei - 1 serotype
Pathogenesis:
• The infection occurs by the ingestion of contaminated
food or drinks (focal-oral contamination).
• It is limited to the GIT without blood invasion.
• They invade the mucosal epithelium causing micro-
abscesses in the wall of the large intestine and terminal
ileum leading to necrosis of the mucous membrane,
superficial ulceration, bleeding, and formation of a
‘pseudomembrane’ on the ulcerated area.
• This consists of fibrin, leukocytes, cell debris, necrotic
mucous membrane, and bacteria.
• Shigellae are highly communicable.
• About 102 organisms can initiate infection
• The IP is short with an onset of abdominal pain,
diarrhoea, tenesmus & fever.
• Recovery occurs spontaneously.
• Shigella produce 2 types of toxins:
– Endotoxin
– Shigella dysentriae Exotoxin:
• Shigellae cause diarrhea (usually bloody), fever,
stomach aches
Diagnosis: Culture:
• Specimen - Fresh stool, mucous flecks, and rectal
swabs.
• Large number of faecal leukocytes & some red
blood cells are seen microscopically.
• The material are streaked on MacConkey media.
• Non-lactose (pale) colonies are identified by
morphology, biochemical reactions & serologically by
agglutination with specific antisera.
YERSINIA
• They are primarily animal pathogens but can
produce serious disease in man.
• Plague is a disease of wild rodents.
• Yersinia includes 3 spp which are pathogenic to
humans.
1. Yersinia pestis is the causative agent of plague.
2. Yersinia enterocolitica
3. Yersinia pseudotuberculosis
• The latter 2 are causative agents of gastroenteritis
with possible involvement of mesenteric lymph
nodes.
YERSINIA PESTIS
Y. pestis
• Causative agent of plague, a serious disease which
used to occur in epidemics.
• Rats & rodents are the natural host of Y. pestis.
• The organism is transmitted to man by rat flea
Xenopsylla cheopis.
Morphology:
• Small gram-negative, stains deeply at ends (bipolar
staining), coccobacilli, non motile & capsulate.
Y. PESTIS
Cultural characters:
• Facultative anaerobe, optimum temp 30oC.
• It grows on nutrient agar, and blood agar.
Antigenic structure:
• All yersiniae possess LPS that have endotoxic activity when
released.
• The organism produce many antigens & toxins that act as
virulence factors.
Virulence factors:
• Fraction I is a capsular antigen, it is antiphagocytic.
• Endotoxic action of LPS.
Y. PESTIS
Pathogenicity
• The organism is highly pathogenic to lab. Animals – rats, mice, guinea pigs
• VW Ag: found in virulent strains, consists of a protein, (V portion),
lipoprotein (the W portion).
• VW is antiphagocytic & promotes the intracellular growth of bacteria.
• Several exotoxins, e.g. murine toxins are lethal to mice
• Pesticin I & pesticin II: bacteriocins produced by Y. pestis - bactericidal for
Y. pseudotuberculosis & some strains of E. coli.
• Transmitted from rat to rat; rat to man by the bite of infected fleas.
• Organism multiplies in the draining LNs causing bubonic plague.
• It can spread to the blood causing septicemic plagues then to the lungs
causing pneumonic plague which can spread from person to person by
droplets.
PLAGUE
Diagnosis:
I. Detection & isolation of the organism from:
1. Aspirate of lymph node in bubonic plague
2. Sputum in pneumonic plague
3. blood by blood culture in septicemic plague
Identification as follows:
• Direct smear stained by gram to demonstrate the bipolar gram-negative
bacilli
• Inoculation on blood agar at 30oC.
• Colonies identified by morphology, biochemical activities,
immunofluorescence by specific antisera & inoculation into white rats.
• Direct injection of sputum or aspirate of lymph nodes into white rats or
guinea pigs.
• Tissue can be examined at autopsy for presence of organisms.
• All cultures are highly infectious.
PLAGUE
II. Serologic diagnosis:
• Convalescent serum antibody titre of 1:16 or greater is evident of Y. pestis
infection - a rising titer is diagnostic.
Treatment:
• Streptomycin is the drug of choice.
• Tetracycline is an alternative.
• They may be used in combination.
Prophylaxis:
The main preventive measures are:
1. Anti-rat and anti-flea measures.
2. Chemoprophylaxis during epidemic by giving tetracycline.
3. A formalin-killed vaccine is used.
4. Live-attenuated vaccine is effective.
PSEUDOMONAS
• Widely distributed in water, soil & sewage
• The genus includes pathogens for animals & plants.
• P. aeruginosa, the major human pathogen of the
group is the third most common cause of
nosocomial infections after S. aureus & E. coli.
• Nearly 30% of hospitalized patients show
colonization.
Antigenic structure:
• Pili extend from the cell surface & promote
attachment to host epithelial cells.
• PS capsule - responsible for the mucoid colonies
seen in culture from pts with cystic fibrosis.
• LPS exist in multiple immunotypes - is responsible for
many of the endotoxic properties of the organism.
Extracellular enzymes:
Most P. aeruginosa produce:
• Exotoxin A - which cause tissue necrosis & is lethal
for animals. It blocks protein synthesis like
diphtheria toxin.
• Other enzymes, e.g. elastases, proteases & 2
hemolysins
Pathogenicity:
• An important cause of hospital acquired infections.
Infections caused by P. aeruginosa
1. UTI:
a. Chronic infections
b. Association with indwelling catheter
2. Burns
3. Septicemia
4. Wound infections
5. Infected skin lesions, e.g.- pressure sores.
6. Chronic OM / otitis externa
7. LRTIs
8. Eye infections secondary to trauma or surgery.
Diagnosis:
Specimens from skin lesions, pus, urine, blood, sputum
are examined.
1. The pus from the lesions may be greenish in colour
2. Smears stained by gram show Gram-ve bacilli
3. Cultures on nutrient agar show the characteristic
greenish colouration of the medium.
• It does not ferment lactose.
• Oxidase test is positive.
Genus Vibrio
• Most vibrios of medical importance are enteric
pathogens of humans.
• Vibrios are wide spread in nature, mainly in water
• V. cholerae which is Gram negative curved bacilli is
the cause of cholera.
• Habitat: water contaminated with patient faeces or
carriers
• G -ve comma-shaped bacilli, arranged in pairs or short
chains giving a spiral appearance.
Toxins:
• Endotoxins & exotoxins are recognized.
• The enterotoxin stimulates persistent and excessive
secretion of isotonic fluid by the intestinal mucosa
• Cholera is an acute infectious disease characterized
by severe vomiting & watery diarrhoea (rice water
stools) resulting in dehydration & collapse.
• The disease is endemic in the Indian subcontinent &
used to occur in world wide epidemics.
Pathogenesis:
• Infection occurs by the oral route through
contaminated food or drinks.
• Source of infection is a case or a carrier who excretes
the organism in the stools.
• IP is short 1-4 days.
• Infection is restricted to intestine with no blood
invasion.
• The organisms attach to the micro villi of the brush
border of epithelial cells where they multiply &
liberate cholera enterotoxin which:
• Binds to ganglioside receptors on the mucosal cells.
• After a lag period of 15-45 minutes adenyl cyclase is
activated & the cAMP concentration inside the
intestinal cells increased.
• Increased intracellular cAMP results in the excretion of
electrolytes such as chloride & bicarbonate ions along
with massive quantities of water.
• Severe diarrhoea & vomiting may lead to dehydration &
death.
• Convalescent carriers occur but chronic carriers are
rare.
Diagnosis of cholera:
A. First case in a non-endemic area
– Specimen for culture: mucous flecks from stools.
1. Stools are inoculated on alkaline peptone water
2. Subcultures are made from the surface pellicle after 6-8 hrs on TCBS
or alkaline agar.
Colonies are identified by:
• A wet mount which is examined for motility.
• Smears stained show G-ve comma shaped bacilli.
• Biochemical activities including cholera red reaction.
• Agglutination with specific anti 01 cholera sera (polyvalent), anti-
Inaba & anti-Ogawa sera.
Treatment:
1. IV fluids to correct the fluid & electrolyte
balance
2. Antibiotics have a secondary role in
treatment. Tetracycline's are the most
effective.
Prevention:
• No specific prophylaxis is available.
• Proper hygienic measures should be followed.
Treatment:
• Restoration of the fluids & electrolyte balance in
severe cases.
• Antibiotics, e.g. sulphonamides, ampicillin &
tetracyclines are effective in treatment.
CAMPYLOBACTER
CAMPYLOBACTER
• Strictly microaerophilic, causes human or animal diarrhoeal
illness are thermophilic,
• Oxidase positive; Grows best at 43oC.
• The main human pathogenic spp: Campylobacter jejuni & C.
coli cause enterocolitis especially in children.
Habitat:
• Various animal including chicken & domestic animals.
Morphology:
• Gram-negative, curved or spiral rods.
• Motile by a single flagellum at one or both poles.
CAMPYLOBACTER
Cultural characters:
• Microaerophilic, grow best in an atm containing a mixture of 5%
O2, 10% CO2, with the remainder an inert gas, usually N2 or H2.
• A simple way to produce the incubation atm. is to place the plates
in an anaerobic jar without the catalyst & to produce the gas with
a commercially available gas-generating pack or by gas exchange.
• Growth takes place at 37oC but the optimal temp of C. jejuni is
43oC
CAMPYLOBACTER
• Media: grow readily on simple media, but selective
media is necessary for isolation from faeces, e.g.
Skirrow's media with vancomycin, polymyxin &
trimethoprim.
• Incubation for 24-48 hrs at 43oC under
microaerophilic conditions.
• Colonies look like spreading fluid droplets.
• Identification is done by Gram-film appearance,
motility, growth temp. requirements 43oC
• C. jejuni & C. coli : sensitive to erythromycin &
nalidixic acid.
HELICOBACTER
HELICOBACTER PYLORI
• Spiral-shaped, Gram negative rod, produce urease,
has multiple flagella at one pole
• Found closely associated with gastric mucosa & is
associated with antral gastritis, gastric & duodenal
(peptic) ulcer dis. & gastric carcinoma.
• It differs in several important biochemical
characteristics from campylobacter spp & does not
grow at 43oC.
Growth characteristics
• Oxidase & catalase positive, motile
HELICOBACTER
Pathogenesis
• Grow optimally at pH 6 -7 but not at pH of gastric lumen
• Found deep in the mucus near the epithelial surface with pH
7.4
• Produce protease that modifies the gastric mucus
• Produce urease –yield ammonia which buffers acid
• Motility helps it to find its way to the epithelial surface
• Destruction of the lumen & glandular atrophy
• Toxins, LPS & ammonia directly damage the cells
HELICOBACTER
Epidemiology
• Is present in the gastric mucosa of 20% in persons <30 years,
but in 40-60% of persons age 60 years
• Developing countries: prevalence about 80% in adults
• Person-to-person transmission is likely
Diagnosis
• Gastric biopsy used for histology used for culture
• Culture – grows in 3-6 days
• Grows optimally at pH 6.0 -7.0 in Skirrow’s medium
• Smear: stained with Giemsa or silver stain
• Serum Ab test
• Special tests: Rapid tests to detect urease activity
HELICOBACTER
Treatment
Triple therapy with:
• Metronidazole and either
• 146Bismuth subsalicylate or Bismuth subcitrate plus
• Amoxicillin or tetracycline - for 14 days eradicates H.
pylori in 70-95% of patients.
• Proton pump inhibitors inhibit H. pylori are urease
inhibitors
Bordetella
Bordetella
• Several spp of the genus cause human infections,
• B. pertussis is the etiologic agent of whooping cough
• B. parapertussis & B. bronchiseptica cause mild
forms of whooping cough in humans.
Bordetella pertussis
• It inhabits the human respiratory tract, usually
associated with acute disease
Morphology:
• Short, gram-negative bacilli
• Fresh isolates are capsulated
BORDETELLA PERTUSSIS
Cultural characters:
• Special enriched media required for primary isolation.
• The common media - charcoal blood agar & bordet-gengou
medium - made selective by the addition of penicillin or
cephalexin
• Growth occurs after 3-5 days of incubation in a moist aerobic
atmosphere at 35oC.
• Colonies are greyish-white with a shiny convex surface;
"mercury drops" appearance.
• Charcoal blood agar is mainly composed of beef extract,
charcoal, starch, nicotinic acid, agar & blood.
• Bordet-gengou medium contains 30% blood, potato extract,
glycerol agar.
B. pertussis
• Bordetella pertussis, the agent of pertussis or whooping cough. Gram
stain. (CDC)
B. pertussis
Antigenic structure: Virulence factors of pertussis
a. Pili:- permit the adherence of B. pertussis to the ciliated
epithelium of the URT
b. Pertussis toxin - promotes phagocytosis.
– The filamentous haemagglutinin mediates adhesion to
ciliated epithelial cells.
– Adenyl cyclase toxin, dermonecrotic toxin, haemolysin -
synthesized & excreted by virulent strain
– Tracheal cytotoxin inhibits DNA synthesis in ciliated cells
c. LPS in the cell wall may also be important in causing damage
to the epithelial cells of the URT
B. pertussis
Pathogenicity:
• B. pertussis cause whooping cough, a highly contagious acute
upper respiratory disease of children.
• Infection occurs by droplets from early cases
• Incubation period: 7-10 days. Stages
• The organism adheres to and multiplies rapidly on the
epithelial surface of the trachea & bronchi and interfere with
ciliary action.
• The bacteria liberate the toxins & substances that irritate
surface cells, causing cough & marked lymphocytosis.
• The most important symptom is cough, which is intermittent
with paroxysmal attacks accompanied by a whoop & is
followed by vomiting
WHOOPING COUGH
• The blood is not invaded.
• Complication: bronchopneumonia, subconjunctival or
cerebral hemorrhage due to paroxysms of severe cough.
• Recovery is followed by long lasting immunity.
Diagnosis:
Specimens: Nasopharyngeal swabs or cough droplets
• On BA the organism grows slowly (3-6 days) to form pinpoint
colon
1. Isolation of organism: positive during the 1st week only
– Collected mucus or droplets are cultured on charcoal
blood agar or Bordet-Gengou media, incubated in humid
atm for up to 5 days
– Colonies that arise are identified by morphology,
immunofluorescence staining or by slide agglutination
with specific antisera
WHOOPING COUGH
2. Direct immunofluorescence:
• used to identify the organism in a smear from the
nasopharyngeal swab.
3. Serologic detection of antibodies:
• Abs start to appear 3 weeks after onset of symptoms.
– CF & agglutination tests are used.
– A rising titre should be detected.
Prophylaxis:
• A heat killed vaccine prepared from capsulated strains of B.
pertussis is given to children during the 1st yr of life in
combination with diphtheria and tetanus toxoida, i.e. as DPT
vaccine.
Treatment:
• Antibiotics: erythromycin is effective if given early
BRUCELLA
• Predominantly infect domestic animals, from which infection
may be transmitted to man causing brucellosis (undulant or
malta fever).
• Brucella spp are highly infectious.
Spp: 6 spp currently recognized in the genus. 4 main spp, each
with a number of biotypes, of concern.
- Brucella abortus causing abortion of cattle.
- B. melitensis causing infection in goats & sheep
- B. suis causing infection in pigs.
- B. canis (in dogs), rare
• Some of the sub types are associated with a particular
geographical location.
BRUCELLA
Habitat:
• Chronic infection in domestic animals.
Morphology:
• Short, slender, pleomorphic, gram-negative bacilli, non motile
& non-spore forming.
Cultural characters:
• Growth on enriched medium such as glucose serum or liver
infusion broth or agar;
• small transparent colonies develop after 2-3 days at 37oC in
aerobic conditions;
• 5-10% CO2 is required for the growth of B. abortus.
BRUCELLA
Biochemical activities:
• Brucella does not ferment any sugar (doesn’t produce
detectable amounts of either acid or gas)
• Indole negative, turns milk alkaline,
• Catalase and oxidase are positive,
• Some biotypes produce H2S gas
• Some are susceptible to growth-inhibitory effect of the dyes,
basic fuchsin & thionine.
Antigenic Structure:
• They all possess 2 antigens: A and M
• A is dominant in B. abortus, M in B. melitensis,
• A & M are almost equal in B. suis.
• In addition, a superficial L Ag (OMP Ag) similar to the
virulence (Vi) antigen of salmonella are present.
BRUCELLA
Virulence factors:
• No toxins, hemolysins or cell wall constituents known to play a
role in the pathogenesis of disease
• Rather the ability of the organism to survive within the host
phagocyte & to inhibit neutrophil degranulation is a major
disease causing factor.
Brucellosis or Undulant fever
• The disease is characterized by bouts of fever that remain for
3-4 weeks alternating with afebrile period of a similar
duration, chills, sweating, headache, muscle pain, weight loss
• The disease run a prolonged course accompanied with
profuse sweating, headache, joint & muscle pains.
BRUCELLA
Route of infection:
• The common routes of infection in humans are;
1. Intestinal tract (ingestion of infected milk)
2. Mucous membrane (droplets)
3. Skin (contact with infected tissues of animals) - Organism
enters through abrasions in the skin or by inhalation.
• Lymphatic dissemination of the bacteria - present in the blood
stream during febrile period.
• As macrophages die, brucellae are released into the blood
stream & establish localised infection in the liver, spleen,
kidneys, bone marrow
BRUCELLA
• Mammary glands in humans & animals infected, brucellae
are shed into breast milk
• Placental & fetal tissues infected in animals - abortion, but
this is not a human phenomenon.
• The reason is due to erythritol in the animal placenta; the
sugar that enhances the growth of brucellae.
Diagnosis of brucellosis (undulant fever )
• Specimens: blood, biopsy (bone marrow, liver), sera for
serology
1. Blood culture:
• Isolation of the organism from the blood by repeated blood
cultures on liver-infusion broth incubated in 5-10% CO2.
BRUCELLA
• Subcultures are done on liver-infusion agar.
• Blood cultures should not be discarded before 4 weeks
incubation
• Isolated organisms are typed by H2S production, dye
inhibition & serologically identified by specific antisera.
2. Serological diagnosis:
• Detection of Abs in the serum of the pts; these appear 7-10
days after the beginning of the fever.
• IgM level rise during the 1st week of illness.
• IgG levels rise about 3 weeks after onset of acute disease &
remain high during chronic disease.
• IgA levels parallel to the IgG levels.
BRUCELLA
a. Brucella agglutination test
- A dilution of pt sera should used (up to 1/1280). A titre of 1/100 -1/200
may be considered of diagnostic significance.
- A second serum sample should be tested to detect a rising titre
b. Blocking antibodies:
• Detected by the Coomb's antiglobulin test. These Abs appear during
the subacute stage of infection, tend to persist for many years.
c. Other serological tests e.g. CFT, RIA & ELISA.
3. Skin tests: ‘Brucellin test’: an intradermal skin test
• A protein extract of brucella is used for ID injection.
• Induration appears within 48-72hrs.
BRUCELLA
Treatment:
– Streptomycin, tetracyclines & ampicillin are effective.
Treatment must be prolonged due to the chronicity of the
disease & intracellular survival of the organism.
Prophylaxis:
1. Live attenuated vaccine used for cattle.
• No vaccine is available for humans.
2. Control of milk supply by pasteurization.
Haemophilus
Important properties
• Haemophilus organisms are small, some times
pleomorphic, and gram-negative bacilli.
• Haemophilus influenzae is the species most
commonly associated with disease.
• However, Haemophilus ducreyi and
Haemophilus aegypticus are less frequently
isolated human pathogens.
HAEMOPHILUS INFLUENZAE
• Cause respiratory disease complications (bronchitis,
pneumonia, otitis media & sinusitis) in pts with viral
influenza
• Present in the nasopharynx of approximately 75% of
healthy children and adults, hasn’t been detected in
other animal.
• Usually the non-encapsulated strains are harbored as
normal flora, but a minority of healthy individuals (3
-7%) intermittently harbor H. influenzae type b
encapsulated strains in the URT.
• Pharyngeal carriage of Hib is important in the
transmission of the bacterium.
Morphology:
• Gram- negative coccobacilli; non-sporing, non motile,
usually capsulated.
Cultural characters:
• Facultative anaerobes, require blood containing media for
their growth such as blood or chocolate agar.
• Most species grow poorly in absence of O2 & growth is
enhanced in atmosphere with added CO2.
• Enriched media are necessary because Haemophilus spp
need one or both of 2 growth factors:
1. Heat stable X factor - haemin or some other iron containing
porphyrin
2. Heat labile V factor - di or tri-phosphopyridine nucleotide
Antigenic structure:
• Smooth capsulated strains can be classified into
6 serotypes (a, b, c, d, e, f) depending on the
capsular polysaccharide.
• H. influenzae type b is the most antigenic.
Possess poly rabitol capsule (PRB)
• Pili and non-pilus adhesions mediate
colonization of the oropharynx with H.
influenzae.
• Cell wall components of the bacteria impair
ciliary function leading to damage of the
respiratory epithelial and endothelial cells and
can enter the blood stream.
Pathogenicity:
• Non capsulated strains are mainly responsible
for exacerbations of chronic bronchitis .
• Capsulated strains (mainly type b) cause
various infections mainly in children aged
from 2 months to 3 yrs
• H.influenzae is responsible for meningitis,
epiglottitis, cellulites, arthritis, otitis media,
sinusitis, lower respiratory tract disease and
conjunctivitis.
Diagnosis of H. influenzae infections:-
Specimens:- pus, sputum, CSF
1. Smears are gram stained. When present in large
numbers in specimen, organism is directly
detected by immunofluorescence or capsule
swelling test.
2. Detection of H. influenzae polysaccharide in CSF
(by counter - immunoelectrophoresis).
3. Culture:- specimens are inoculated on chocolate
agar. Colonies are identified by their morphology,
inability to grow except on blood containing
media, i.e. assays in detection of X & V factors
and serologically typed with specific antisera.
HAEMOPHILUS DUCREYI
• Causes chancroid / soft sore - an ulcer on the
external genitalia - STD.
• The chancre is soft, unlike the hard chancre of
syphilis.
• Draining lymph nodes are tender & enlarged.
Diagnosis:
• Smears made from lesions or material aspirated
from lymph nodes, show G -ve coccobacilli that
may be intracellular.
• It is possible to grow the organism with difficulty
on blood containing media (chocolate agar).
Treatment:
• Sulphonamides & streptomycin - used
successfully in treating the infection.
SPIROCHETES
• Large heterogenous group of spiral shaped, motile
organisms
Habitat:
• Most are free living & non pathogenic, but few cause
important human diseases.
Morphology:
• Spirochetes have unique helical structure:
– Central protoplasmic cylinder bounded by the
cytoplasmic membrane
– Cell wall of similar structure to that of gram
negative bacteria.
• The axial filaments regarded as internal flagella
Consist of three genera that are medically important
1. Treponema causes syphilis, yaws & pinta.
2. Borrelia causes relapsing fever & Lyme dis.
3. Leptospira causes leptospirosis (Weil's dis).
• The genus treponema includes few pathogenic
members.
Treponema
• Treponema pallidum is the most important & is the
causative organisms of syphilis.
• Many commensal spp occur in the mouth & genitalia.
Morphology:
• Slender, with spiral coils regularly spaced 1um apart
• They are actively motile by means of an axial filament
Treponema pallidum
• The treponemes replicate by transverse
fission, the cells may remain joined to each
other.
• Treponema spp are not stained with Gram,
but can be seen by dark-ground microscopy
in unstained preparations, fluorescent-
labeled Ab, or silver stain is needed to
demonstrate the spiral morphology.
Disease
Syphilis
1. Primary syphilis:
• The bacteria enter the body through tiny breaks in
the skin & mucous membranes.
• The treponemes enter the lymphatics, the regional
lymph nodes become involved, and bacteraemia
occurs.
• Chancre develops, at the site of inoculation, 6-12
wks after exposure to infection as a papule on the
genitalia which ulcerates, not painful, which heals
spontaneously.
2. Secondary syphilis:-
• Lesions occur 6-12 weeks after the appearance of
the chancre & are characterized by generalized
manifestations, e.g. skin rash.
• T. pallidum is found in large numbers in the lesions of
both primary & secondary stages and highly
infectious.
• About 25% of patients are cured, 25% progress to the
tertiary stage
3. Tertiary syphilis:-
• Cellular immune response to T. pallidum & its
metabolic products.
• Characterized by appearance of gummata in the
internal organs 5-40 yrs after initial infection, if not
treated.
• CNS involvement as manifested by tabes dorsalis &
paralysis.
• Cardiovascular lesions causing aortic aneurism are
common
Syphilis
Lab Diagnosis:
I. Detection of sphirochaetes in the lesion
– A wet mount is prepared from exudate collected
from the chancre in primary stages & from the skin
eruptions & mucous patches in secondary stages.
a. Dark-ground microscope shows living motile
spirochaetes with a characteristic slow
movement & angulation.
b. Direct immunofluorescence using fluorscein
labeled anti-treponema Abs.
II. Serologic diagnosis (STS): These are either
treponemal or non-treponemal antigens.
BORRELIA
• Many members of the genus are commensals.
• Pathogenic borrelia cause relapsing fever & lyme
disease.
• Lice or ticks become infected by feeding on patient's
or rodent's blood during the bacteraemia stage.
Morphology:
• Large spirals with irregular coils.
• The coils are irregularly spaced 2-4um apart.
• Motility is by both a rotating & a twisting motion.
• They are stained with ordinary stains & are gram-
negative, also stained with blood stain as Giemsa or
Wright's stain.
BORRELIA
Cultural characters:
• They can be cultured in the fluid media containing
blood, serum or tissue.
Antigenic structure:
• Borreliae are antigenically variable
• B. recurrentis show antigenic variation in vivo.
Borreliae isolated from different hosts or vectors are
designated as strains of B. recurrentis.
Relapsing Fever
• A disease characterized by repeated bouts of fever
alternating with periods of apyrexia.
• It is caused by B. recurrentis and its variants.
Relapsing Fever
• Epidemic relapsing fever is transmitted by lice while
endemic RF is transmitted by ticks. Rodents are reservoir
for the organism
• Borrelia multiplies in the blood of the insect & infection
is transmitted by their bite or by rubbing crushed lice or
ticks into bite wounds.
• After an IP of 3-10 days, there is sudden onset of fever
which lasts for about 4 days followed by a febrile period
of 3-10 days when the pt develops another bout of fever.
• The organism is found in large numbers in the blood
during the febrile stage.
• Abs against Borrelia appear during the febrile stage;
these agglutinate & destroy the organism and the attack
is terminated.
• Antigenic variants of Borrelia emerge, cause the relapse.
Relapsing Fever
Diagnosis:
• Blood is obtained during the rise in temperature for smear &
animal inoculation.
1. During the febrile stage: Blood films stained with leishman or
Giemsa stain reveal large numbers of loosely coiled
spirochetes among red cells.
2. During the afebrile stage: The organism is scanty in the blood &
blood films are negative.
• Diagnosis is done by injecting white mice IP with 1-2ml
patient's blood. After 2-4 days, films from tail blood are
stained & examined for presence of borrelia.
• The animal acts as in vivo enrichment medium.
Relapsing Fever
3. Serological diagnosis:
• Complement fixation test (CFT) is used
patients may have positive VDRL.
Treatment:
• by penicillin, tetracyclines, erythromycin &
chloramphenicol.
• Jarisch Herxheimer reaction is produced
following antibiotic treatment.
Mycobacteria
• Mycobacteria are rod shaped, aerobic bacteria that
do not form spores.
• Several members produce disease in man and
animals while others are saprophytes.
The commoner spp are classified into:
1. The typical tubercle bacilli: M. tuberculosis, M. bovis
2. The atypical or environmental mycobacteria
(opportunistic pathogens) - found in water, soil,
animals and man, without evidences of disease.
3. M. leprae.
Mycobacterium tuberculosis
Morphology:
• Thin straight or slightly curved rods.
• They can not be stained by simple stains due to their
high lipid content including mycolic acids (long chains
fatty acids), waxes and phosphatides.
• In the cell, the lipids are largely bound to proteins &
polysaccharides.
• When stained by Ziehl-Neelsen stain, they appear as
thin pink rods arranged singly or in small groups.
• Once stained, they resist decolouriziation with 20%
H2SO4 & alcohol.
Cultural characters:
• Mycobacteria are strictly aerobes.
• They grow on egg - enriched media such as
Lowenstein-Jensen (LJ) medium containing a
selective agent (malachite green), so it is a selective
as well as enriched medium.
• They grow very slowly; no growth appears before 2-4
weeks incubation at 37oC.
• The growth on LJ medium is irregular, dry and
yellowish in colour.
Animal pathogenicity:
• Both M. tuberculosis & M. bovis are pathogenic to
guinea pigs.
• When injected sc, a local nodule develops and
ulcerates within 4-6 weeks.
• It is associated with enlargement of the draining L
nodes.
• Rabbits are more susceptible to M. bovis, which
causes generalized fatal infection than M.
tuberculosis, which causes mild local lesions.
• The disease can affect any organ of the body.
• M. bovis is transmitted by ingestion of milk from
infected cattle and cause intestinal tuberculosis.
Pathogenesis:
• M. tuberculosis produces no recognized toxins.
• The disease results from the multiplication and local
invasion at the site of infection.
• The organism is capable of multiplying intracellularly
stimulating CMI & hypersensitivity which leads to
tissue damage.
• The resulting pathology depends on whether the
disease is a primary infection, a reinfection or
reactivation.
• Infection with M. tuberculosis confers on the pt 2
conditions, resistance and hypersensitivity.
• Immunity & hypersensitivity are the features of CMI
to TB.
Transmission
• Human TB is caused by M. tuberculosis
and M. bovis.
• M. tuberculosis is transmitted by droplets
Diagnosis of tuberculous infections:
• Diagnosis depends on detection and
identification of the tubercle bacilli (TB) in,
and their isolation from pathologic specimens.
Specimen:
• TB can affect every tissue in the body; thus the
type of specimen for examination varies widely.
• Sputum is examined for diagnosis of PTB
• Urine sample for renal tuberculosis,
• CSF for meningeal tuberculosis,
• stools for intestinal tuberculosis, etc.
• The following steps are made for detection or
isolation of TB from sputum.
Direct smears:
– Specimens: stained with Ziehl-Neelsen stain.
– The detection of AFB in sputum gives a fairly
strong indication of PTB, but are detected only if
they are present in large numbers.
– The smear may be stained by auramine O and
examined by the fluroescent microscope for
yellow fluorescing tubercle bacilli.
– Negative specimens are repeated for 3
successive days and re-examined after
concentration.
Treatment:
The policy in treatment of tuberculosis requires:
1. Prolonged treatment: There is a slow response of
TB treatment and it should be continued for 6-12
months (DOTs = 6-8 mo).
This is because:
a. Most bacilli are found intracellular
b. The caseous material interfere with the drug.
c. In chronic lesions TB bacilli are not dividing, i.e.
"metabolically inactive", hence resistant to drugs,
2. Combination of drugs due to:
a. The prolonged course of treatment needed, which
may lead to toxicity, and
b. The rapid emergence of resistant strains.
– Combination of drugs should be used to reduce
toxicity and resistance.
– The drug of choice are isoniazide (INH), rifampicin,
streptomycin, para-amino-salicylic acid &
ethambutol.
Prevention:
A.Public health measures
• Early Dx of cases and their treatment until they
become non-infectious.
• Control of infection from milk by pasteurization of
milk.
B. Vaccination:
• A live-attenuated vaccine – BCG commonly used.
• It is prepared from bovine strain with a fixed very low
virulence.
• This attenuated strain was obtained by repeated
subculture of the organism in media containing bile.
• The vaccine is given in a single dose of 0.1ml
containing 1-2 million organisms ID in the deltoid
region. The aim is to create a controlled focus which
stimulates hypersensitivity and CMI against infection
with both human & bovine types.
• BCG is nowadays used to stimulate non specifically
CMI in certain tumors.
MYCOBACTERIUM LEPRAE
• M. leprae - causes Hansen’s disease / leprosy in
man, which affects mainly the mucous membrane
of the nose, skin and nerve fibers.
Morphology:
• They are similar in size & shape to the TB bacilli.
• They are acid fast, only to 5% H2SO4 which is used
for decolourization. They are also alcohol fast.
Pathogenesis
• Leprosy (Hansen’s disease) is caused by
M.leprae. Intracellular pathogens replicate
within skin histocytes, endothelial cells, and
the schwann cells of nerves. Two distinct
forms of leprosy – tuberculoid and
lepromatous exist.
tuberculoid leprosy
– the cell-mediated response to the organism limits
its growth
– very few acid-fast bacilli are seen
– granulomas containing giant cells form
– the lepromin skin test result is positive
lepromatous leprosy
– the cell – mediated response to the organism is
poor
– the skin and mucus membrane lesions contain
large numbers of organisms
– foamy histocytes rather than granulomas are
found
– the lepromin skin test result is negative.
– Note that in lepromatous leprosy, only the cell-
mediated response to M.leprae is defective
Treatment
• Dapsone with or with out rifampin is used to
treat the tuberculoid form of disease
• clofazimine is added for the treatment of the
lepromatous form.
• Therapy is given for longer period.
Prevention and Control
• Chemoprophylaxis with dapsone for exposed
children is recommended.
• Disease is controlled through the prompt
recognition and treatment of infected people.
Mycoplasma
• Formerly pleuropneumonia-like organisms (PPLO)
because they were first described as causing
pleuropneumonia in cattle.
Properties of Mycoplasma
• Mycoplasma are among the smallest living mos capable
of independent existence.
• No rigid cell wall, but are composed of a small unit of
cytoplasm enclosed in a protein - lipid membrane.
Normal habitat:
• Wide spread in nature being found in soil, plants and the
mucous surfaces of animals.
• In humans, M. hominis & U. urealyticum can be found in
the lower urogenital tract, mouth and throat
• M. pneumoniae can be found in the respiratory tract.
M. pneumoniae
• Causes pulmonary disease – upper respiratory
illness, sore throat, ear infections, atypical
pneumonia (characterized by slow onset, fever,
headache, malaise, non-productive cough).
• Expectorated sputum is mucoid; contains
neutrophils, bacterial cell are not visible on Gram
stain.
Treatment
• Mycoplasma are sensitive to tetracyclines and
erythromycin.
• They are resistant to penicillin & cephalosporins
because mycoplasma lack cell walls and these drugs
interfere with bacterial cell wall synthesis.
Chlamydiae
• Chlamydiae consists of 4 spp that cause a variety of
disease including genital and RT infections.
• They are non-motile & form intracellular inclusions in
the host cell that can be seen by light microscope.
• They reproduce in the cytoplasm of host cells and
cannot survive outside the cell due to their limited
metabolic capacity.
• They use ATP produced by the host cell to fuel their
metabolic reactions.
• They possess both RNA & DNA, differentiating them
from viruses
• have cell walls similar in structure to G-ve bacteria.
Chlamydiae
Species of chlamydiae
• Chlamydia trachomatis
• Chlamydia psittaci
• Chlamydia pneumoniae
• Chlamydia pecorum
Chlamydia trachomatis
• Chlamydia trachomatis is an obligate intracellular
bacterium with 15 immunotypes, as follows:
Chlamydia trachomatis
1. A- C cause trachoma endemic in Africa, Asia)
– Within the spp, there are different serotypes of C.
trachomatis: A, B, Ba, C - associated with trachoma, a
preventable form of blindness.
2. Serotypes L1, L2, L3
– Associated with LGV - STI that results in inflammation
of genital tract LNs - genital ulcer in tropical countries.
3. Serotypes D-K: associated with genital tract infection
(urethritis,cervicitis, epididymitis, proctitis, endometritis
,Inclusion conjunctivitis )
Chlamydia pneumoniae
• Human pathogen that causes respiratory tract
infection.
• The genetic make-up of C. pneumoniae varies from
the other 3 spp of chlamydia. There is less than 10%
similarity between C. pneumoniae and other spp
• Pneumonia caused by C. pneumoniae is sometimes
referred to as walking pneumonia.
Chlamydia psittaci
• Ubiquitous among spp of birds and is common in
domestic mammals.
• Infection in birds usually involves the gastrointestinal
tract, and is shed in feces.
• Humans can become infected through exposure to
infected birds (psittacosis).
• Cats can develop respiratory tract infection (feline
pneumonitis) and in cattle, infection may result in
abortion (bovine abortion).
Rickettsiae
• obligate intracellular bacteria transmitted to humans
by arthropods vectors
• e.g. lice, ticks & fleas, that play important roles in their life
cycles.
• They share some antigens proteins with other spp
• C. burnetii :– rickettsia- like bacterium that causes
systemic diseases.
• Pathogenic rickettsiae: typhus, spotted fever and scrub
typhus group.
Morphology:
• Rickettsiae are pleomorphic, G-ve,
coccobacilli, better stained with Giemsa
(appear blue) & with maccchiavello stain
(appear red).
• They have cell walls made up of
peptidoglycans resembling those of G -ve
bacteria
Rickettsiae
Pathogenesis:
• Rickettsiae enter the body through the bite or feces
of an infected arthropod vector.
• They enter endothelial cells by induced phagocytosis,
multiply intracellularly & destroying their host cells.
• The bacteria invade vascular epithelial cells &
become widely disseminated.
• Human infection results from inhalation of dust
Rickettsiae
Basic features of ricketsiae and C. burnetii
• Rickettsiae & C. burnetii resemble viruses in that they
are mostly obligate parasites and are unable to
survive as free living organisms.
• They are about the size of the largest viruses & can
be seen with the light microscope.
• Unlike viruses, they contain both RNA and DNA,
multiply by binary fission, have cell walls that contain
muramic acid, possess enzymes, and show sensitivity
to antiseptics & antibiotics.
Rickettsiae
Toxic properties:
• Rickettsiae contain toxins that produce death in
animals within a few hours after injection.
Disease caused by Rickettsiae:
• Rickettsial infections are characterized by fever,
headache, malaise, skin rash & enlargement of the
liver and spleen.
• The rash is due to focal areas of infection that cause
hyperplasia & inflammation of the vascular
epithelium. the result is thrombosis & blockage of
the small blood vessels.
Rickettsial Diseases
1. Epidemic typhus:
• Occurs in epidemics & is transmitted by body louse.
• Initial symptoms of the disease are headache and fever
6-15 days after being exposed to R. prowazekii.
• Macular rash start after 4-6 days of illness on the trunk
and axillary folds & then spread to the extremities
• The mental state of the patient may progress from
dullness to stupor and, in very severe cases, even coma.
• Prompt treatment may be life saving.
• The disease is fatal especially in old age.
• The Weil Felix reaction is positive with proteus OX-19.
Rickettsial Diseases
Brill-Zinsser disease
• Relapse of louse-borne typhus that commonly
occurs many years after the primary infection.
• The syndrome is milder & of short duration than
the primary disease.
• Precipitating factors as those lowering the
immunity may lead to reactivation of latent
infection.
• R. prowazekii remains sequestrated in cells of
reticuloendothelial system.
• Antibody titre to proteus OX-19 are absent. Such
individuals are immune to a 2nd infection.
Rickettsial Diseases
2. Murine typhus (endemic typhus):
• The causative organism is R. typhi.
• The clinical picture is in common with that of
epidemic typhus, the disease is milder and is rarely
fatal except in elderly patients.
• The vector for human infection is the rat flea.
Human is accidental hosts.
• The disease rambles louse-borne typhus in
pathogenesis, symptomatology & serology.
Rickettsial Diseases
3. Tick-borne spotted fever
• Has clinical similarities among the tick-borne
rickettsioses of the spotted fever group.
• The most severe is Rocky Mountain spotted fever.
Causative organism is R. rickettsii.
• The spotted fever resembles typhus clinically;
however, unlike the rash in other rickettsial diseases,
the rash of the spotted fever group usually appeared
first on the extremities before spreading to the trunk.
• The appearance of the rash on the pales & palms of
the feet is considered diagnostic.
Rickettsial Diseases
• Vascular damage in severe cases may result in
haemorrhagic rash, hypotensive shock, pulmonary
edema & impairment of CNS function.
• Infection with spotted fever group rickettsiae confers
long lasting immunity.
• Several species of ticks are the natural vectors of
Rocky Mountain Spotted Fever, each prevails in a
particular region.
• R. rickettsii is transferred transovarially in ticks.
• The Weil-Felix reaction is positive with porteus OX-19
and OX-2.
Rickettsial Diseases
4. Rickettsial Pox:
• Caused by R. akari, a mild infection transmitted by
mites.
• The clinical course is similar to other spotted fever
group infections (fever, headache and eschar at the
site where the infected mite fed).
• The rash is first maculopapular but becomes
vesicular. The rash resembling that of varicella.
• Patients usually recover;
• The disease is transmitted from animal to human by
a rodent mite.
• The major reservoir of rickettsial pox is the house
mouse
• Control of mice is best method of disease prevention
Rickettsial Diseases
5. Scrub typhus:
• It is caused by R. tsutsugamushi, and humans
become infected from larvae of rodent mites called
chiggers.
• The disease resembles epidemic typhus clinically.
• One feature is the eschar, the punched-out ulcer
covered with a blackened crust that indicates the
location of the mite bite.
• Generalized lymphadenopathy & lymphocytosis are
common. Cardiac & central involvement may be
severe.
• Antibody titers to proteins OX-K can be detected.
Rickettsial Diseases: Q fever
6. Q fever
• caused by Coxiella burnetii, an atypical rickettsial disease.
• The bacteria are resistant to dryness, survive for months
outside the host cell this may be due to endospore formation.
• Human disease is acquired by the respiratory route rather
than by the bite of an arthropod.
• By inhalation of dust contaminated with rickettsiae from dried
feces, urine or milk or from aerosols in slaughter houses.
• The disease resembles influenza, non-bacterial pneumonia,
hepatitis or encephalopathy rather then typhus.
• There is no rash or local lesion.
• The Weil-Felix test is negative, but there is a rise in titre of
specific antibodies to C. burnetii detected by
immunofluorescence assay.
• Rarely infective endocarditis develops in Q fever.
Rickettsial Diseases
7. Trench fever
• Caused by Rochalimaa quintana, which are closely
resemble Rickettsiae.
• They can grow in cell-free media, grow on blood
agar in 10% CO2.
• Patients have fever, chills, headache, myalgia & is
apparent when individuals are severely stressed &
infested with large numbers of body lice.
Rickettsial Diseases
Lab diagnosis:
Microscopy:
• In tissue preparation, rickettsiae can be stained with
Giemsa or Macchiavello stains.
Culture:
• Embryonated egg inoculation techniques are used.
Serology:
• Most rickettsial disease are usually diagnosed
serologically - specific IgM Abs are produced
followed in the later stages by an IgG response.
• The IgG persist in the serum for several years.
• Immunity against louse-borne typhus and spotted
fever lasts for about one year after infection.
Rickettsial Diseases
1. Prevention of transmission by breaking the chain of
infections.
a. Epidemic typhus: Delousing with insecticide.
b. Murine typhus: Rat- proofing building and using rat
poisons.
c. Scrub typhus: Clearing from campsites the
secondary jungle vegetation in which rats and mites
live.
d. Spotted fever: clearing of infested land, personnel
prophylaxis in the form of protective clothing such as
high boots, socks worn over trousers; tick repellents;
and frequent removal of attached ticks.
e. Rickettsial pox: Elimination of rodents and their
parasites from human houses.
Rickettsial Diseases
2. Prevention of transmission of Q fever:
• By adequate pasteurization of milk. "High temp,
short time" pasteurization at 71.5oC for 15 sec are
adequate to destroy viable coxiella.
3. Prevention by vaccination:
• Active immunization has been used with
formalinized antigens prepared from the yolk sacs of
infected chick embryos or from cell cultures.
• These vaccines have been prepared for:
– Epidemic typhus (R. prowazekii)
– Rocky Mountain (R. rickettsi)
– Q fever (Coxiella burnetti)

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systemic bacteriology (7)............pptx

  • 1. GETNET AYALEW(BSc., MSc.) UoG, CMHS, School of Biomedical and Lab. Sciences Department of Medical Microbiology
  • 3. Introduction • The human body is inhabited by thousands of different bacterial species, some living transiently, others in a permanent parasitic relationship. • Likewise, the environment that surrounds us, including the air we breathe, water we drink, and food we eat, is inhabited by bacteria, many of which are relatively avirulent and some of which are capable of producing life threatening diseases.
  • 4. • The systemic bacteriology is aimed to improving your understanding of the – Important bacterial pathogens – The disease they cause – Pathogenesis – Laboratory diagnosis – Treatment options – Prevention and control measures
  • 6. STAPHYLOCOCCUS General characteristics  Staphylococcus: staphyle, meaning ‘bunch of grapes’  S. aureus are widely distributed in nature and cause infections of varying severity; some are members of the normal flora  There are about 33 spp of Staphylococci  Species of medical importance: – S. aureus – S. epidermidis – S. saprophyticus
  • 8. Staphylococcus aureus Cultural characters: • Facultative anaerobes • Grow on nutrient agar producing golden yellow colonies of 1-2 mm(MSA) • Produce disease through:- - ability to multiply & invade tissue - Production of extracellular enzymes & toxins • produce β-haemolytic colonies on blood agar.
  • 10. Antigenic composition S. aureus cell wall components & antigens: • Teichoic acid, protein A: – It binds to Fc portion of IgG, used in co-agglutination. • Capsule in some strains, make it more virulent surface receptors for bacteriophages that permit ‘phage typing’ for epidemiologic purposes • Coagulase - causes the clumping of non-capsulated strains when mixed with a solution containing fibrinogen, e.g. plasma.
  • 11. Enzymes & toxins produced by S. aureus: 1. Coagulase production – Most definitive virulence factor of S. aureus 2. Cytotoxins: α, β, γ toxins and P-V leukocidin, δ Haemolysins: – cause lysis of RBC of many animal spp demonstrated as β-hemolysis on blood agar. 3. Exfoliative toxin: – Cause the desquamation seen in SSSS in young children- produced by phage group II strains
  • 12. 4. Toxic shock syndrome toxin (TSST-1): – Produced by strains that cause the toxic shock syndrome (manifest by fever, shock, etc) 5. Enterotoxins: – Toxins are heat stable and resistant to the action of gut enzymes – They cause diarrhoea & vomiting associated with staphylococcal food poisoning. 6. Other toxins and enzymes include: – Leukocidin - Staphylokinase – Proteinase - Lipase – Catalase - Hyaluronidase
  • 13. Diseases produced by S. aureus: A. Focal suppuration(pus) and abscess formation: 1. Superficial infection: – Folliculitis, carbuncles, boils, stye, mastitis, abscess formation 2. Deep-seated lesions: – Osteomyelitis, septic arthritis, endocarditis, meningitis, endocarditis, bronchopneumonia, empyemia, etc. 3. Bacteraemia with multiple abscesses in tissues. – Outbreaks of hospital wound infections commonly occur due to antibiotic resistant staphylococci.
  • 14. B. Toxin-mediated staphylococcal diseases 1. Food poisoning – Results from ingestion of preformed enterotoxin in contaminated food that is improperly cooked and kept unrefrigerated for some time. – Source of contamination of food: the hands or nose of a cook / food handlers /carriers. – Types of food involved in staphylococcal food poisoning are carbohydrate rich foods, e.g. cakes, pastry, milk, etc. – IP: short (1-8 hrs) followed by nausea, vomiting, diarrhoea and general malaise with no fever.
  • 15. 2. Toxic shock syndrome (TSS): – This is associated with TSST-1, first described in menstruating women using tampons. The syndrome also occurs with wound or localized infections. – TSS has an abrupt onset of fever, vomiting, diarrhoea, muscle pains, rash Hypotension, heart and renal failure may occur in severe cases. 3. Staphylococcal scalded skin syndrome (SSSS): – Occurs due to the exfoliative toxin produced by phage II strains of S. aureus. – The syndrome occurs in babies and young children. – It is characterized by large areas of desquamation of the skin and generalized bullae formation.
  • 16. Menstruation-associated TSS Less than 5% of women carry S. aureus in their vaginal flora only one in five have the potential to produce TSST-1.
  • 17. FIGURE . Evidence of staphylococcal scalded-skin syndrome in a 6-year-old boy. Nikolsky’s sign, with separation of the superficial layer of the outer epidermal layer, is visible.
  • 18. Laboratory diagnosis: Specimens – Swabs from lesions: pus, sputum, CSF, blood, urine examined Gram stain smears: Gram positive cocci in clusters Culture: – S. aureus colonies show complete haemolysis on blood agar and golden yellow
  • 20. Coagulase negative staphylococci (CoNS) S epidermidis – Inhabitant of the skin. – It is involved in indwelling catheters, prosthetic materials, shunts, surgery – It is a common cause of prosthetic heart valve endocarditis – It also causes nosocomial bacteremia – Often multiple antibiotic resistance - Methicllin
  • 21. S. saprophyticus • Commonly isolated from animals and their carcasses. • S. saprophyticus is resistant to the antibiotic Novobiocin, a characteristic used in Lab. to distinguish it from S. epidermidis • It is a 2nd most common cause of UTI, after E. coli in young women accounting for 10-20% . • It also causes soft tissue infections
  • 22. STREPTOCOCCUS • General feature – Non-motile, non-spore forming, catalase-negative Gram positive cocci arranged in chains. – Widely distributed in nature, some are commensals in the throat, intestine. – Others cause human diseases – Others found in water, dust, milk /milk products. – Most are facultative anaerobes – More than 30 spp are identified.
  • 23. • Scanning electron microscope image of Streptococcus
  • 24. Streptococcus Classification: • Heterogenous group of bacteria I. According to their O2 requirements – aerobic – anaerobic II. according to their action on RBC in blood agar – Beta haemolytic streptococci: complete haemolysis (clear zone around the colonies on BA) e.g. S. pyogenes, S. agalactiae – Alpha haemolytic streptococci: partial haemolysis e.g. Viridans streptococci, S. pneumoniae – Non-haemolytic or gamma streptococci: no haemolysis/ change in RBC's, e.g. Enterococci
  • 25. III. based on serologic reactivity of cell wall polysaccharide Ags (group c carbohydrate ) • Also known as Lancefield groups – Group A - S. pyogenes – Group B - S agalactiae – Group C - S. equisimilis – Group D - Enterococci – Group H - S. Sanguis – Group K - S. salivarius
  • 26. Streptococcus pyogenes • Known as Group A streptococcus (GAS) • The most important human pathogen causing diseases including: – Suppurative conditions / Skin infections – Throat infections – Systemic infections – Non-suppurative sequelae • About 5-15% of normal individuals harbor the bacterium, in their respiratory tract, without signs of disease.
  • 27. Virulence factors of group A streptococci: 1. M -protein, fibronectin-binding proteins (e.g. F protein) & lipoteichoic acid for attachment 2. Hyaluronic acid capsule: inhibits phagocytosis 3. Exotoxins such as pyrogenic toxin, cause the rash of scarlet fever & systemic toxic shock syndrome 4. Invasins - Streptokinase, streptodornase (DNase B), hyaluronidase & streptolysins
  • 28. Pathogenesis: Diseases due to toxins 1. Streptococcal sore throat and follicular tonsillitis (pharyngitis) – It is characterized by enlarged tonsils with purulent exudates, high fever and enlarged cervical lymph nodes 2. Impetigo: A local infection of the skin characterized by formation of blisters which break leaving surface covered with pus or crusts
  • 29. II. Diseases due to invasion: • Diffuse rapidly spreading infections that involve the lymphatics with minimal local suppuration infection can extend to the blood stream. 1. Puerperal sepsis: • Infection of the uterus after delivery or abortion leading to endometritis and is associated with bacteremia.
  • 30. 2. Soft tissue sepsis: • Wound infection, cellulitis, lymphadenitis, necrotizing fascitis - may be complicated by streptococcal septicemia. 3. Acute Bacterial Endocarditis: • The organism reaches the heart valve through the blood stream as a complication of any of the primary lesions mentioned before.
  • 31. III. NONSUPPURATIVE SEQUELAE: • Post-streptococcal diseases –GN, RF – May occur 1- 4 weeks following a primary inadequately treated group A streptococcal infection of the skin & Respiratory Tract • Acute glomerulonephritis (AGN): – The condition is due to Ag-Ab complex deposition on the glomerular basement membrane (GBM). – The majority of patients recover completely. However few may die or pass to chronic GN & renal failure.
  • 32. Rheumatic fever (RF): • The condition is due to Ag-Ab complex deposition on the heart valves. • The onset follows 1-4 weeks after throat infection with group A streptococci. • The most serious complication of streptococcal throat infection since it may result in damage of the heart valves & muscle
  • 33. Lab diagnosis of streptococcal diseases: Specimens: Swabs from throat or other lesions, pus, or blood in case of bacteraemia method – Direct smears stained by Gram’s method show Gram-positive cocci in chains. – Cultures done on blood agar show colonies producing complete haemolysis – Blood cultures: done for bacteremic infections e.g. bacterial endocarditis & puerperal sepsis.
  • 34. Streptococcus agalactiae • Group B streptococci (GBS) • out 10% - 30% of pregnant women are colonized with GBS in the genital tract. • GBS causes life-threatening infections in newborn infants • GBS can also cause serious diseases in pregnant women, the elderly, and adults with other illnesses. • In newborns, GBS is the most common cause of sepsis and meningitis and a common cause of pneumonia. • GBS disease in newborns usually occurs in the first week of life.
  • 35. Diagnosis • Lab test of blood or spinal fluid. Treatment • Newborns and adults are usually treated with antibiotics given IV
  • 36. Enterococcus • 12 spp, some of these are - Enterococcus faecalis, E. fecium, S. durans, and S. avium • They are normal inhabitants of the intestine. • They cause UTI, wound, cholecystitis blood infections, meningitis, bacteremia (neonates) subacute endocarditis, prostatitis. • Enterococci are among the most common causes of nosocomial infections, esp in ICU
  • 37. STREPTOCOCCUS PNEUMONIAE /Pneumococcus/ Habitat: • normal inhabitant of the human upper respiratory tract (found as commensal) • The carrier rate of S. pneumoniae in the normal human nasopharynx is 20-40%. Morphology: • Gram-positive, catalase-negative, lancet-shaped slightly elongated and arranged in pairs and non- motile • Are capsulated in animal tissues.
  • 38. Pathogenesis: • S. pneumoniae does not produce toxins • It owes its virulence to the capsule, which enables the organism to invade the tissues and resist phagocytosis. • Predisposition to disease: if the resistance is lowered, e.g. by viral respiratory infections, excessive smoking, alcoholism, malnutrition Diseases caused by S. pneumoniae • S. pneumoniae is currently the leading cause of invasive bacterial disease in children and the elderly. • Causes 80% of lobar pneumonia; conjunctivitis, paranasal sinusitis, meningitis, acute exacerbation of chronic bronchitis, septic arthritis, osteomyelitis, endocarditis, peritonitis, cellulitis, brain abscess.
  • 39. Laboratory diagnosis of lobar pneumonia: 1. Direct microscopic examination of gram stained sputum smears will show the prevalent organism to be pneumococci. 2. Sputum cultured on blood agar. Treatment • Pneumococci are sensitive to many antibiotics. • Some isolates have recently been reported to be resistant to penicillin.
  • 40. Prophylaxis / Prevention: 1. Pneumococcal conjugate vaccine (PCV7) – for infant immunization children, 2. Polyvalent polysaccharide vaccine (PPV23) – for adults - are safe and fairly effective. – The later is recommended for specially susceptible individuals, e.g. aged (>65 years), debilitated or bed-ridden patients or after splenectomy.
  • 41. 4.2. GRAM NEGATIVE COCCI Genus Neisseria • Important properties – The genus Neisseria contains gram-negative cocci that resemble paired kidney beans. – There are two important human pathogens: • Neisseria meningitidis • Neisseria gonorrhoeae – Named after a germ physician aleksandre Nissere – All Neisseriae are oxidase – positive; i.e. they possess the enzyme cytochrome C.
  • 42. NEISSERIA GONORRHOEAE (GONOCOCCI) • They cause gonorrhoea, a STD of humans. • Gonococci attack mucus membrane of the GUT, eye, rectum, throat producing acute suppuration that may lead to tissue invasion followed by inflammation and fibrosis. • Gonorrhea is generally limited to superficial mucosal surfaces lined with columnar epithelium
  • 43. Antigenic structure & virulence factors: • Pili • LoS • Proteins • IgA protease
  • 44. Diseases 1. Gonorrhoea: – It is a VD transmitted by sexual intercourse. – It affects both males & females. – The IP for gonorrhea is 2-8 days after sexual contact. a. Males: – gonorrhoea is usually in the form of acute anterior urethritis with purulent urethral discharge and painful urination. – The organism may also invade the prostate resulting in prostatitis or extend to the testicles resulting in orchitis. • The involvement of testicles,
  • 45. b. Females: – gonorrhoea is in the form of cervicitis & urethritis with major symptoms include mucopurulent vaginal discharge and mild lower abdominal pain. – It may extend to the uterine tubes causing salpingitis, fibrosis & infertility. – Asymptomatic males & females are major problem as unrecognized carriers of the disease. – About 50% of women with cervical infections are asymptomatic.
  • 46. • May affect young girls through contaminated towels or toilet seats causing vulvovaginitis. • Cervical involvement may extend through the uterus to the fallopian tubes resulting in salpingitis, or to the ovaries resulting in ovaritis. • About 15% of women with uncomplicated cervical infections may develop PID • Involvement of fallopian tubes or ovaries may result in sterility.
  • 47. 2. Ophthalmia neonatorum: • An infection of the new born acquired from the birth canal of gonorrhoeal mother. • It may involve the cornea leading to blindness. 3. Occasionally, disseminated infections occur.
  • 48. Diagnosis: Acute urithritis (male): • Urethral discharge examined by direct Gram stain • Presence of G -ve diplococci intra- & extracellularly in pus cells Chronic male; acute and chronic female infection: - • Morning drop or prostatic discharge in chronic male infection
  • 49. Cervical discharge in acute and chronic female infections are examined by: 1. Direct Gram stain - usually hard to detect the organism due to the presence of normal flora or due to low No. 2. Cultures done on chocolate or Thayer-martin media incubated at 37oC in atm of 5-10% CO2. Left: Neisseria gonorrhoeae Gram stain of pure culture; Right: Neisseria gonorrhoeae Gram stain of a pustular exudate.
  • 50. Treatment • Due to emergence of penicillin resistant beta- lactamase producing strains, antibiotics now used are:- spectinomycin, tetracyclines & chloramphenicol Prevention: • Involves the use of condoms & the prompt treatment of symptomatic patients. • Neonatal ophthalmia is prevented by use of tetracycline or erythromycin eye ointment immediately after birth.
  • 51. NEISSERIA MENINGITIDIS (MENINGOCOCCI) • Highly contagious disease, usually occurs in epidemics • Capsular polysaccharide Ags; according to which the meningococci are classified into groups. • The most important groups associated with disease in man: A, B, C,Y and W-135 strains . • Epidemics in Africa are mainly due to group A.
  • 52. NEISSERIA MENINGITIDIS Properties of polysaccharide Capsule: • It enhances virulence by its antiphagocytic action. • It is the Ag that defines the serologic -groups. • It is the Ag detected in the spinal fluid of patients with meningitis. • It is the Ag in the vaccine that induces protective immunity.
  • 53. MENINGITIS • The disease occurs in epidemics among young adults. • The organism occurs in the nasopharyx of healthy carriers. • The carrier rate is 3-30%. During epidemics, the carrier rate reaches 80%. • It starts in the nasopharynx where it remain silent or gives rise to exudative pharyngitis. • From the nasopharynx the organism may invade the blood stream (meningococcemia) causing high fever, haemorrhagic skin rash etc.
  • 54. • The infection is transmitted by droplets from cases or carries. • Hemorrhagic necrosis of Adrenal glands – Waterhause - Friderichsen syndrome characterized by high fever, shock, widespread purpura, disseminated intravascular coagulation and adrenal insufficiency. • Severe bacteremia may be fatal due to circulatory collapse & suprarenal hemorrhage. • From the blood stream, the organism reaches the meninges causing meningitis manifested by fever, severe headache, vomiting and rigidity of the neck and back muscles. • It may progress to coma within few hours.
  • 55. Diagnosis 1. CSF test • In meningitis, the CSF is turbid due to the large number of pus cells; 20,000/ul. a. The CSF is centrifuged and the deposit is examined microscopically after Gram stain • The presence of gram negative diplococci intracellular in pus cells is diagnostic. b. The deposit is cultured on chocolate agar or Thayer- Martin medium and incubated at 37oC in 5-10% CO2. C. Detection of meningococcal polysaccharide Ag in CSF by co- agglutination:- 2. Blood Culture may give positive results.
  • 56. Prophylaxis: • Rifampicin 600 mg orally twice daily for 2 days can eradicate the carrier state and serve as chemoprophylaxis for contacts. Vaccination: • Polyvalent vaccine from the capsular polysaccharide of groups A, C, Y & W-135 strains available • It is effective in preventing epidemics of meningitis & reduce the carrier rate. • The vaccine does not include the Group B polysaccharide which is poorly immunogenic in humans. • Trials are being made to prepare a recombinant vaccine.
  • 57. 4.3. GRAM POSITIVE RODS They are grouped into: 1. Spore forming – Bacillus specius (B. Ceruse, B. anthracis ) – Clostridium species • C. Tetani • C. Perfringens • C. botulinum • C. Difficile 2. Nonspore forming – Corinobacterium species – Listeria species
  • 58. THE GENUS BACILLUS Bacillus: • Aerobic, G+ve, endospore forming bacilli, occur in chain • Ubiquitous in nature - soil, water and airborne dust. • Most spp of are harmless saprophytes (anthracoids) • Two spp - Bacillus anthracis & B. cereus - are important pathogenic members.
  • 59. Bacillus anthracis Pathogenicity: The virulence of B. anthracis is dependent upon both presence of the capsule and production of the toxin.
  • 60. Bacillus anthracis Anthrax • Primarily a disease of animals (sheep, cattle, horses) causing septicemia & death • Humans accidentally contract the dis by contact with infected animals or their products. There are 3 clinical types: 1. Cutaneous anthrax: (95%) – It occurs in butchers, farmers & veterinarians. – Organisms enter through small abrasions, multiply locally producing a malignant pustule 2. Pulmonary anthrax (wool sorter's disease): – Rare disease, occurs by inhalation of spores. – It occurs in persons who handle wool or animal hairs.
  • 61. Bacillus anthracis 3. Intestinal anthrax: • Very rare; organisms ingested in infected meat with invasion and ulceration of the GI mucosa. • From all these sites invasion of the blood stream may occur giving rise to septicemic anthrax. Lab diagnosis: • Samples taken from skin, sputum, stool, blood. Direct smears: • Gram stain - demonstrate G +ve rectangular long bacilli arranged in long chains with clear zone representing the capsule. • The polychrome methylene blue stains the organism blue while the capsule appears pink
  • 62. Bacillus anthracis Culture • Organism grows on simple & enriched media Animal inoculation • In mice or guinea pigs, helpful to differentiate between anthrax & anthracoids. Serologic tests • Precipitating and haemagglutinating Abs demonstrated in sera of man and animals. Treatment • The antimicrobial of choice: penicillin • Tetracycline, erythromycin be used in pts with allergy to penicillin
  • 63. Bacillus anthracis Prevention: 1. Disposal of animal carcases by burning or by deep burial in lime pits. 2. Autoclaving of animal products. 3. Protective clothing & gloves for handling potentially infected materials. 4. Active immunization of domestic animals with live - attenuated vaccines. 5. High risk persons immunized with a non-living vaccine
  • 64. B. cereus Bacillus cereus • Motile, causes toxin-mediated food poisoning after consumption of cooked rice with enterotoxin • Toxins released by the bacteria lead to vomiting and diarrhea (symptoms similar to S. aureus food poisoning) 1. Diarrheal type – Characterized by diarrhea & abdominal pain occurring 8-16 hrs after consumption of the contaminated food. – Associated with a variety of foods including vegetable dishes, meat, sauces, pastas, desserts, dairy products
  • 65. B. cereus 2. Emetic disease – Nausea & vomiting begin 1-5 hrs after the contaminated food is eaten. – Boiled rice and held for prolonged periods at ambient temp, then quick-fried before serving is usual offender – Dairy products or other foods are occasionally responsible. – Frequently misdiagnosed as staph food poisoning.
  • 66. GENUS CLOSTRIDIA Clostridia: – Strictly anaerobic, Gram-positive spore forming bacilli Natural habitat: the intestinal tracts of animals & humans; the spore are present in the soil. Pathogenic clostridia: • Nearly 100 Clostridium spp identified, but only 25 -30 commonly cause human or animal disease. • Different groups according to the diseases they produce: 1. C. tetani - cause tetanus 2. C. perfringens - cause gas gangrene, food poisoning 3. C. botulinum - cause food poisoning 4. C. difficile - cause enterocolitis.
  • 67. CLOSTRIDIUM TETANI • Found in the intestine of man, animals & in manured soil. • It causes tetanus in man & animals. Morphology: • Gram-positive, long, chain bacilli with round terminal spores giving the characteristic ‘drum-stick’ appearance. • They are motile. Cultural characters: • Strict anaerobes, grow on nutrient agar on which colonies are surrounded by a clear zone of haemolysis due to its tetanolysin toxin. • The organism grows on Robertson cooked medium.
  • 68. CLOSTRIDIUM TETANI Antigenic structure: • The neurotoxins produced by all toxigenic strains of C. tetani are serologically identical. • 10 types of antigenic variation among flagella identified. Pathogenicity: • Human dis caused by tetanospasmin (neurotoxic exotoxin) • Toxins are produced by vegetative cells of C. tetani • Toxin production appears to be under a control of plasmid gene.
  • 69. CLOSTRIDIUM TETANI a. Tetanospasmin – Acts upon the CNS; inhibits release of acetyl choline - thus interfering with muscular transmission – Toxin binds to ganglioside receptors; blocks release of inhibitory mediators (eg. glycine) at spinal synapses, lead to generalized muscular spasm & hyperflexia. b. Tetanolysin - haemolytic toxin, is of minor importance in the pathogenesis of tetanus. – Infection occurs by contamination of wounds with street dust containing spores. – At the local site of infection the spores germinate.
  • 70. TETANUS • Injury: e.g. nail prick, surgical wound, gun shot wound, infected umblical stump leading to tetanus neonatorum. • Germination of the spores & development of vegetative organisms that produce toxin are aided by: necrotic tissue, calcium salts, associated pyogenic infections • The disease is characterized by convulsive tonic contractions of voluntary muscles. • Spasm in jaw muscles lead to trismus (lock jaw).
  • 71. TETANUS Diagnosis: • Rests on the clinical picture & history of contaminated wounds. • Wound exudate are examined microscopically for the presence of gram-positive bacilli with drum-stick appearance. • The exudate is cultured on blood agar & incubated anaerobically, on Robertson cooked meat medium. • The organism is identified by its pathogenicity to laboratory animals.
  • 72. TETANUS Treatment: 1. Antitoxin given at once to suspected cases, without waiting for lab. diagnosis, in order to neutralize the toxin before it fixes to CNS. 2. Antibiotics: Penicillin is given in big doses to inhibit the growth of C. tetani & stops further toxin production. It may also control associated pyogenic infection.
  • 73. TETANUS Prophylaxis • Tetanus is a totally preventable disease. Active immunization: • Alum precipitated tetanus toxoid is given as ‘DPT’ in 3 IM injections at the age of 2,4 & 6 months. • Booster doses given to military personnel before / during war, for pregnant women to guard against labor infection & to provide maternal immunity for the new born
  • 74. TETANUS Passive immunization: • Antitoxin given to wounded persons, without previous history of vaccination. • Antitoxin prophylaxis should be accompanied by active immunization with tetanus toxoid.
  • 75. CLOSTRIDIUM PERFRINGENS Clostridia that produce invasive infections • C. perfringens - commonest of members of the genus clostridium associated with gas gangrene. • Found in the colon of 25-35% of healthy people, under certain conditions produce serious, life treating infections • C. perfringens type A & C produce enterotoxin which are responsible for food poisoning. Morphology: • Gram-positive large bacilli, the only non-motile spp in the genus, spores are oval, sub-terminal, non projecting • Capsules are formed in tissues.
  • 76. C. perfringens Toxins or virulence factors • C. perfringens produce a variety of toxins & enzymes that result in spreading of infection. 1. α-toxin (lecithinase) - acts on lecithin which is a component of the cell membrane. 2. Theta toxin has a haemolytic & necrotizing effect. 3. DNase, hyaluronidase & collagenase 4. Enterotoxin produced by some strains (types A & C) causes food poisoning following ingestion of warmed meat dishes. • Toxin is released in the gut causing diarrhoea after 6-18 hrs which lasts for 1-2 days.
  • 77. C. perfringens Gas gangrene • Several species of clostridia may cause gas gangrene, but the commonest is C. perfringens. Pathogenesis: • Infection occurs when wounds are contaminated with soil containing the organism or its spores the condition occurs in deep lacerated, devitalized wounds as in car accidents or war wounds. • The presence of foreign bodies, mixed infection with aerobic pyogenic bacteria, decreased blood supply - lowers O2 tension, favours germination of spores
  • 78. GAS GANGRENE • Vegetative cells multiply, ferment sugars producing gas - distends the tissues and interferes with blood supply leading to tissue death. • Necrotising toxin, collagenase & hyaluronidase favour necrosis and spread of infection. • Proteolytic clostridia digest dead tissues leading to change in colour & foul odour of the wound. • This is accompanied by generalized toxemia, fatal Diagnosis: • Primarily on clinical grounds. • Bacteriological confirmation from wound exudate & swabs from deeper areas • Direct smear are stained by gram - large G+ve rods
  • 79. GAS GANGRENE Prevention: • Prevention depends upon adequate cleaning of contaminated wounds, surgical removal of foreign bodies & excision of all devitalized tissues. • Administration of antibiotics specially penicillin. • Antitoxic sera for passive prophylaxis is unreliable. • Toxoids not available for active immunization.
  • 80. CLOSTRIDIUM BOTULINUM C. botulinum • Saprophyte in soil frequently present in the intestinal tract of domestic animals. Morphology: • Gram-positive large straight rods, motile, non capsulate, spores are oval central or sub-terminal. Pathogenesis: • C. botulinum causes botulism produced by ingestion of the neurotoxin in contaminated canned meat or fish. • C. botulinum does not replicate easily within the body. • Such foods provide proper anaerobic conditions for growth & production of exotoxin.
  • 81. C. botulinum Typing: • 8 serotype (A-H) known, each with a serologically distinct, but pharmacologically similar toxin. • Human botulism is usually due to types A, B & E. Cultural characters: • Strict anaerobe, grows on simple media. • Wound botulism can occur in rare cases when devitalized tissue is contaminated with soil. • Intestinal botulism in infants, known as floppy baby syndrome, is due to ingestion of spores, followed by germination & toxin production in the gut. • The feeding of honey has been implicated as a possible cause of infant botulism.
  • 82. C. botulinum Toxin: • It is the most potent poison known. • During growth of C. botulinum & during autolysis of the bacteria, toxin is liberated into the environment. • It acts by preventing release of acetyl choline at motor nerve ending in the parasympathetic system; destroyed in 2 min at 60-90oC, dependent on type. BOTULISM • An intoxication resulting from ingestion of canned food containing neurotoxin produced by C. botulinum. • The toxin has affinity to the cranial motor nerves causing bulbar paralysis • Death results from respiratory or cardiac failure. • There is no diarrhoea or vomiting.
  • 83. C. botulinum Diagnosis: • Toxin can be demonstrated in serum from the patient • The antigenic type of toxin identified by neutralization with specific antitoxin in mice. Mice die rapidly. • C. botulinum grown from left over food and tested for toxin production (rarely done). • In infant botulism, C. botulinum & toxin can be demonstrated in stools but not in serum. • Toxin may be demonstrated by passive hemagglutination or RIA Treatment • Rapid administration of polyvalent antitoxin. Prevention • by careful sterilization of food before canning.
  • 84. CLOSTRIDIUM DIFFICILE • Present in the gut of up to 3% of healthy adults, 66% of infants • C. difficile infection is the most important cause of hospital-acquired diarrhea. Antibiotic-associated Enterocolitis • It is associated with antibiotic-induced pseudo- membranous colitis which is the severest form of antibiotic associated diarrhoea, • Most common antibiotics are ampicillin & clindamycin. • The antibiotics disturb the balance of bacteria in the gut, C. difficile multiply rapidly, produce toxins, cause illness
  • 85. Corynebacterium Important properties – Non-spore forming, non-acid fast gram-positive bacilli with club – shaped (wider at one end) and are arranged in palisades or in V-or L-shaped formations. – Their arrangements may resemble Chinese letters. – They are aerobic or facultative anaerobic, non-motile and Catalase positive organisms. – Although many species of corynebacteria can function as opportunistic pathogens, the most commonly associated human pathogen is Corynebacterium diphtheria
  • 86. Corynebacterium diphtheriae Pathogenesis • Lysogenic beta phages are able to produce the diphtheria toxin because the phage carries the toxin gene. • Major significant virulence factor produced by C. diphtheriae is the diphtheria toxin, which is entirely under the genetic control of the beta- phage. The toxic is an A-B toxin. It has a B or binding portion and an A or enzymatically active portion.
  • 87. Epidemiology • Humans are the only natural host of C. diphtheriae. • Aerosol dissemination spreads the organism from person to person. • Rarely by direct contact. • The organism can also infect the skin especially in the tropics but can occur world wide in persons with poor skin hygiene. Disease • Most prominent sign of diphtheria is thick, gray, adherent pseudo membrane over the tonsils and throat. • There are three prominent complications. – Extension of the membrane in to the larynx and trachea, causing airway obstruction. – Myocarditis accompanied by arrhythmias and circulatory collapse.
  • 88. Laboratory diagnosis 1. Microscopy- Metachromatic granules in bacteria stained with methylene blue is important 2. Culture- Specimens collected from the nasopharynx and throat are inoculated on to – Media developed specifically for this organism (eg., Cyateine –tellurite agar, serum Tellurite agar, Loffler’s medium). 3. Serology-Toxins A and B can be identified in faeces by a latex bead agglutination test.
  • 89. Treatment • The treatment of choice is antitoxin; it should be given immediately to neutralize unbound toxin in the blood. Penicillin G or erythromycin is recommended also but neither is a substitute for antitoxin. Prevention • Symptomatic diphtheria can be prevented by actively immunizing people with diphtheria toxoid during child hood and booster dose given every 10 years through out life.
  • 90. Listeria • Important properties – The genus Listeria is a small gram positive, non- spore forming facultative anaerobic bacilli. – The genus consists of seven species, with Listeria monocytogenes the only human pathogens.
  • 91. Listeria monocytogenes • Listeria preferentially grows intracellular, and cell mediated immunity is a more important host defense than hummoral immunity. • It is distributed world wide and found in plants, soil and in many domestic animals from which it may be found in their milk and on their flesh. • Transmission is associated with consumption of contaminated food products such as poorly cooked meats and unpasteurized milk and cheese.
  • 92. Disease • Infection during pregnancy can cause abortion, premature delivery or sepsis during the peripartum period. • Meningitis or sepsis can occur in immunocompromised adult. • Gastroenteritis caused by consumption of contaminated dairy products & under cooked meats is the major health problem.
  • 93. Laboratory diagnosis • Gram-positive rods, small, motile gray colonies with a narrow zone of beta -hemolysis on blood agar plate suggest the presence of Listeria. • Identification of the organism as L. monocytogens is made by sugar fermentation tests. Treatment • Invasive disease can be treated by ampicillin with or without gentamicin. • Trimethoprim-sulfamethoxazole is an alternative drug.
  • 94. Prevention and control • Limiting the exposure of immunocompressed patients to potential sources such as infected animals and their products and contaminated vegetable is recommended. • There is no vaccine available to date.
  • 95. 4.4. Gram negative rods Natural habitat – the intestinal tract of humans & animals – Gram-negative, facultative anaerobic bacilli – About 32 genera, contains >130 spp – Some genera (e.g. Escherichia, Shigella, Salmonella, Enterobacter, Klebsiella, Serratia, Proteus, etc). – Some enteric pathogens, e.g. E. coli, are part of the normal flora & incidentally cause disease, – Others: Salmonella & Shigella are regularly pathogenic for humans. Morphology: – Gram-negative bacilli, non-motile or motile by peritrichous flagella; non-sporing, some encapsulated.
  • 96. Escherichia coli • Normal inhabitants of the intestine of man & animals. • Some cause disease in humans. Morphology • Gram-negative bacilli, motile, some strains are capsulated. Cultural characters • Facultative anaerobes, grow on simple media, • On MacConkey medium, they produce rose-pink colonies due to Lactose Fermentation .
  • 97. Virulence factors: • Many strains of E. coli have powerful toxins responsible for disease. • Pili (adhesive factors)
  • 98. Diseases caused by Escherichia coli :- 1. UTI: – E. coli is the commonest cause of UTI. – Uropathogenic E. coli colonize the vagina & periurethral region from where they ascend to the bladder or kidney causing cystitis or pyelonephritis. 2. Intestinal diseases: – Different strains of E. coli can cause diarrhoea through different mechanisms:
  • 99. a. Enterotoxigenic E. coli (ETEC): - Certain serotypes, e.g. 06,078 cause traveller's and infantile diarrhoea. - The diarrhoea is watery & ranges from mild to severe cholera - like and may be fatal. – The organism adheres to intestinal epithelium through the pili or colonization factors. Then they liberate enterotoxins. – The toxin cause diarrhoea by stimulating guanyl cyclase in intestinal mucosal cells.
  • 100. b. Enteropathogenic E. coli (EPEC):- –Certain serotypes e.g. O55, O111 cause outbreaks of neonatal diarrhoea in nurseries. –They act mainly by adhering tightly to intestinal mucosa resulting in loss of microvilli & cupping of cells around the bacteria. – Thus preventing the normal functions of absorption & secretion.
  • 101. c. Enteroinvasive E. coli (EIEC): – Certain serotypes e.g. O124, O164 cause dysentery - like diarrhoea through invasion of intestinal epithelial cells. d. Enterohaemorrhagic E. coli (EHEC):- – Certain serotypes e.g. O157. These strains produce verocytotoxin (VT). – These strains cause haemorrhagic colitis which is severe form of diarrhoea with bloody discharge. Produce shiga toxin
  • 102. 3. Neonatal meningitis: E. coli causes 40% of neonatal meningitis followed by group B streptococci. 4. It causes bacteraemia & endotoxic shock in immunocompromised host. 5. It causes hospital-acquired infections Diagnosis: • Specimen according to the site of infection e.g. urine, pus, stools, CSF etc. • Pathologic material is inoculated on MacConkey media; LF colonies are further identified by their morphology & biochemical reactions.
  • 103. ENTEROBACTER • Occurrs as indigenous intestinal flora. • It is similar to klebsiella in many biochemical characters; however, it is motile. Species • E. aerogenes - has small capsules • Found in intestine or free • Causes UTI and sepsis
  • 104. CITROBACTER • Similar to E. coli except in being citrate positive. • It antigenically resembles the salmonellae. • It is seen as opportunistic pathogen in immunocompromised individuals • Causes UTI, sepsis, wound infection, osteomyelitis & gastroenteritis in elderly hospitalized patients. • Cases of neonatal meningitis also have been reported. • Spp: C. freundii, C. koseri
  • 105. KLEBSIELLA • Normal inhabitants of the intestine & upper respiratory tract. • Are saprophytes in soil & water, some cause disease in man. Morphology: • Gram-negative bacilli, non motile and capsulated. Cultural characters: • They ferment glucose, lactose, with production of acid & gas.
  • 106. Diseases caused by Klebsiella 1. K. pneumoniae – causes lobar pneumonia. – It cause hospital-acquired infections, eg UTI. 2. K. rhinoscleromatis causes rhinoscleroma which is a granulomatous lesion (chronic granuloma) of the nose & throat /oropharynx. 3. K. ozane: rhinitis 4. K. oxytoca: cause UTI, RTI, wound sepsis
  • 107. PROTEUS • Are normal inhabitants of the intestine of man. • They cause infections only when they leave the intestine. The important members are: • Proteus mirabilis: cause UTI • Proteus vulgaris: nosocomial infections Morphology: • Gram-negative bacilli very pleomorphic (variable in length) and highly motile.
  • 108. Cultural characters: • They grow on nutrient agar producing a spreading growth "swarming". Proteus forms colourless colonies on MacConkey agar Biochemical activities: • They are urease positive (i.e. decompose urea rapidly • ferment glucose with production of acid & gas, • produce H2S
  • 109. Disease Proteus mirabilis is the most frequently isolated spp. 1. UTI: Urinary urea is "split" by the bacterial urease to produce ammonium salts: this results in alkaline urinary pH & an increased risk of urinary calculi. 2. Often isolated from mixed flora of wounds, burns, pressure sores, chronic discharging ears. 3. Septicaemia. Treatment: • Proteus are highly resistant to antibiotics & antibiotic • Sensitivity tests should be done before treatment. • P. mirabilis is inhibited by penicillin • Other members: aminoglycosides & cephalosporins
  • 110. SALMONELLAE • The natural habitat is animal gut. • Predominantly, animal pathogens which can also cause disease in man. • Food stuffs from animal sources are important vehicles in the transmission of infection. • There are 2 species and more than 2500 serotypes within the genus salmonella, 4 of them; S. typhi, S. paratyphi A, B and C cause enteric fever in man. • Other species cause salmonella food poisoning or enterocolitis e.g. S. typhimurium and S. enteritidis.
  • 111. SALMONELLAE Antigenic structure: • They posses O (somatic) and H (flagellar) Ags. Pathogenesis & Diseases caused by salmonellae: • They cause a variety of conditions, referred as salmonellosis. 1. Enteric fever 2. Enterocolitis 3. Bacteraemia and septicaemia. Typhoid fever (Enteric fever ) • Produced by S. typhi, S. paratyphi A, B & C. • Source of infection is stool or urine of cases or carriers. • Infecting dose is about 105 organisms
  • 112. • The organism enters the body by the oral route in contaminated food or drinks, e.g. raw vegetables, fruits, raw shell fish & milk products. • After ingestion, the organism multiplies in payer's patches, • passes through the lymphatics to the blood stream causing bacteraemia that persist for one week. • It then disseminates to the kidney & is excreted in urine, & to the liver & is excreted in bile to reach the intestine.
  • 113. Clinical features: • IP 10 -14 days • fever, malaise, headache, constipation & myalgia with enlargement of the liver & spleen. • The fever is a gradually rising (in a step ladder fashion). • After recovery some individuals continue to harbour salmonella in their tissues as convalescent or chronic carriers. • They carry the organism in the gall bladder or urinary tract & intermittently excrete it in the stools /urine. • Such individuals should not work as food handlers.
  • 114. Diagnosis of enteric fever: 1. Isolation of the organism from blood, urine & stools 2. Detection of Abs in the serum of the patient. 3. Serological diagnosis(widal test )- used to identify antibody in patients Prevention 1. Sanitary measures must be taken to prevent contamination of food and water. 2. Carriers must not be allowed to work as food handlers. Treatment: • The drugs of choice are chloramphenicol, ampicillin & trimethoprim-sulfamethoxazole.
  • 115. II. Salmonella Enterocolitis • Many members of salmonella are responsible for this condition. • The most important are S. typhimurium & S. enteritidis. • These organisms are common pathogens of animals or birds. Transmission: • The organism is transmitted from improperly cooked meat of infected animals, eggs of infected birds or from food contaminated with rat excreta.
  • 116. Symptoms: • The disease is characterized by nausea, vomiting, abdominal discomfort, diarrhoea & slight fever. • The condition occurs after multiplication of the organism in the intestine, i.e. it is an infection and not due to a toxin. • The incubation period is 12-18 hrs to allow for such multiplication. • Recovery follows within 1week.
  • 117. III. Septicaemia • Salmonella septicaemia is characterized by prolonged fever & anaemia. • Following oral infection, there is early invasion of the blood stream with possible focal lesions in the form of osteomyelitis, pneumonia, meningitis or endocarditis.
  • 118. Shigellae • The natural habitat limited to the intestinal tracts of humans & other primates, where they cause bacillary dysentery. • They are closely related to E. coli. • Non-motile & non-capsulated. • They produce pale non-lactose fermenting colonies on MacConkey media.
  • 119. Antigenic structure: • According to the somatic O Ags shigellae are divided into 4 serogroups or species and numerous serotypes:- - S. dysentriae - 13 serotypes - S. boydii - 18 serotypes - S. flexneri - 6 serotypes - S. sonnei - 1 serotype
  • 120. Pathogenesis: • The infection occurs by the ingestion of contaminated food or drinks (focal-oral contamination). • It is limited to the GIT without blood invasion. • They invade the mucosal epithelium causing micro- abscesses in the wall of the large intestine and terminal ileum leading to necrosis of the mucous membrane, superficial ulceration, bleeding, and formation of a ‘pseudomembrane’ on the ulcerated area. • This consists of fibrin, leukocytes, cell debris, necrotic mucous membrane, and bacteria.
  • 121. • Shigellae are highly communicable. • About 102 organisms can initiate infection • The IP is short with an onset of abdominal pain, diarrhoea, tenesmus & fever. • Recovery occurs spontaneously. • Shigella produce 2 types of toxins: – Endotoxin – Shigella dysentriae Exotoxin: • Shigellae cause diarrhea (usually bloody), fever, stomach aches
  • 122. Diagnosis: Culture: • Specimen - Fresh stool, mucous flecks, and rectal swabs. • Large number of faecal leukocytes & some red blood cells are seen microscopically. • The material are streaked on MacConkey media. • Non-lactose (pale) colonies are identified by morphology, biochemical reactions & serologically by agglutination with specific antisera.
  • 123. YERSINIA • They are primarily animal pathogens but can produce serious disease in man. • Plague is a disease of wild rodents. • Yersinia includes 3 spp which are pathogenic to humans. 1. Yersinia pestis is the causative agent of plague. 2. Yersinia enterocolitica 3. Yersinia pseudotuberculosis • The latter 2 are causative agents of gastroenteritis with possible involvement of mesenteric lymph nodes.
  • 124. YERSINIA PESTIS Y. pestis • Causative agent of plague, a serious disease which used to occur in epidemics. • Rats & rodents are the natural host of Y. pestis. • The organism is transmitted to man by rat flea Xenopsylla cheopis. Morphology: • Small gram-negative, stains deeply at ends (bipolar staining), coccobacilli, non motile & capsulate.
  • 125. Y. PESTIS Cultural characters: • Facultative anaerobe, optimum temp 30oC. • It grows on nutrient agar, and blood agar. Antigenic structure: • All yersiniae possess LPS that have endotoxic activity when released. • The organism produce many antigens & toxins that act as virulence factors. Virulence factors: • Fraction I is a capsular antigen, it is antiphagocytic. • Endotoxic action of LPS.
  • 126. Y. PESTIS Pathogenicity • The organism is highly pathogenic to lab. Animals – rats, mice, guinea pigs • VW Ag: found in virulent strains, consists of a protein, (V portion), lipoprotein (the W portion). • VW is antiphagocytic & promotes the intracellular growth of bacteria. • Several exotoxins, e.g. murine toxins are lethal to mice • Pesticin I & pesticin II: bacteriocins produced by Y. pestis - bactericidal for Y. pseudotuberculosis & some strains of E. coli. • Transmitted from rat to rat; rat to man by the bite of infected fleas. • Organism multiplies in the draining LNs causing bubonic plague. • It can spread to the blood causing septicemic plagues then to the lungs causing pneumonic plague which can spread from person to person by droplets.
  • 127. PLAGUE Diagnosis: I. Detection & isolation of the organism from: 1. Aspirate of lymph node in bubonic plague 2. Sputum in pneumonic plague 3. blood by blood culture in septicemic plague Identification as follows: • Direct smear stained by gram to demonstrate the bipolar gram-negative bacilli • Inoculation on blood agar at 30oC. • Colonies identified by morphology, biochemical activities, immunofluorescence by specific antisera & inoculation into white rats. • Direct injection of sputum or aspirate of lymph nodes into white rats or guinea pigs. • Tissue can be examined at autopsy for presence of organisms. • All cultures are highly infectious.
  • 128. PLAGUE II. Serologic diagnosis: • Convalescent serum antibody titre of 1:16 or greater is evident of Y. pestis infection - a rising titer is diagnostic. Treatment: • Streptomycin is the drug of choice. • Tetracycline is an alternative. • They may be used in combination. Prophylaxis: The main preventive measures are: 1. Anti-rat and anti-flea measures. 2. Chemoprophylaxis during epidemic by giving tetracycline. 3. A formalin-killed vaccine is used. 4. Live-attenuated vaccine is effective.
  • 129. PSEUDOMONAS • Widely distributed in water, soil & sewage • The genus includes pathogens for animals & plants. • P. aeruginosa, the major human pathogen of the group is the third most common cause of nosocomial infections after S. aureus & E. coli. • Nearly 30% of hospitalized patients show colonization.
  • 130. Antigenic structure: • Pili extend from the cell surface & promote attachment to host epithelial cells. • PS capsule - responsible for the mucoid colonies seen in culture from pts with cystic fibrosis. • LPS exist in multiple immunotypes - is responsible for many of the endotoxic properties of the organism. Extracellular enzymes: Most P. aeruginosa produce: • Exotoxin A - which cause tissue necrosis & is lethal for animals. It blocks protein synthesis like diphtheria toxin. • Other enzymes, e.g. elastases, proteases & 2 hemolysins
  • 131. Pathogenicity: • An important cause of hospital acquired infections. Infections caused by P. aeruginosa 1. UTI: a. Chronic infections b. Association with indwelling catheter 2. Burns 3. Septicemia 4. Wound infections 5. Infected skin lesions, e.g.- pressure sores. 6. Chronic OM / otitis externa 7. LRTIs 8. Eye infections secondary to trauma or surgery.
  • 132. Diagnosis: Specimens from skin lesions, pus, urine, blood, sputum are examined. 1. The pus from the lesions may be greenish in colour 2. Smears stained by gram show Gram-ve bacilli 3. Cultures on nutrient agar show the characteristic greenish colouration of the medium. • It does not ferment lactose. • Oxidase test is positive.
  • 133. Genus Vibrio • Most vibrios of medical importance are enteric pathogens of humans. • Vibrios are wide spread in nature, mainly in water • V. cholerae which is Gram negative curved bacilli is the cause of cholera. • Habitat: water contaminated with patient faeces or carriers • G -ve comma-shaped bacilli, arranged in pairs or short chains giving a spiral appearance.
  • 134. Toxins: • Endotoxins & exotoxins are recognized. • The enterotoxin stimulates persistent and excessive secretion of isotonic fluid by the intestinal mucosa • Cholera is an acute infectious disease characterized by severe vomiting & watery diarrhoea (rice water stools) resulting in dehydration & collapse. • The disease is endemic in the Indian subcontinent & used to occur in world wide epidemics.
  • 135. Pathogenesis: • Infection occurs by the oral route through contaminated food or drinks. • Source of infection is a case or a carrier who excretes the organism in the stools. • IP is short 1-4 days. • Infection is restricted to intestine with no blood invasion. • The organisms attach to the micro villi of the brush border of epithelial cells where they multiply & liberate cholera enterotoxin which: • Binds to ganglioside receptors on the mucosal cells.
  • 136. • After a lag period of 15-45 minutes adenyl cyclase is activated & the cAMP concentration inside the intestinal cells increased. • Increased intracellular cAMP results in the excretion of electrolytes such as chloride & bicarbonate ions along with massive quantities of water. • Severe diarrhoea & vomiting may lead to dehydration & death. • Convalescent carriers occur but chronic carriers are rare.
  • 137. Diagnosis of cholera: A. First case in a non-endemic area – Specimen for culture: mucous flecks from stools. 1. Stools are inoculated on alkaline peptone water 2. Subcultures are made from the surface pellicle after 6-8 hrs on TCBS or alkaline agar. Colonies are identified by: • A wet mount which is examined for motility. • Smears stained show G-ve comma shaped bacilli. • Biochemical activities including cholera red reaction. • Agglutination with specific anti 01 cholera sera (polyvalent), anti- Inaba & anti-Ogawa sera.
  • 138. Treatment: 1. IV fluids to correct the fluid & electrolyte balance 2. Antibiotics have a secondary role in treatment. Tetracycline's are the most effective.
  • 139. Prevention: • No specific prophylaxis is available. • Proper hygienic measures should be followed. Treatment: • Restoration of the fluids & electrolyte balance in severe cases. • Antibiotics, e.g. sulphonamides, ampicillin & tetracyclines are effective in treatment.
  • 140. CAMPYLOBACTER CAMPYLOBACTER • Strictly microaerophilic, causes human or animal diarrhoeal illness are thermophilic, • Oxidase positive; Grows best at 43oC. • The main human pathogenic spp: Campylobacter jejuni & C. coli cause enterocolitis especially in children. Habitat: • Various animal including chicken & domestic animals. Morphology: • Gram-negative, curved or spiral rods. • Motile by a single flagellum at one or both poles.
  • 141. CAMPYLOBACTER Cultural characters: • Microaerophilic, grow best in an atm containing a mixture of 5% O2, 10% CO2, with the remainder an inert gas, usually N2 or H2. • A simple way to produce the incubation atm. is to place the plates in an anaerobic jar without the catalyst & to produce the gas with a commercially available gas-generating pack or by gas exchange. • Growth takes place at 37oC but the optimal temp of C. jejuni is 43oC
  • 142. CAMPYLOBACTER • Media: grow readily on simple media, but selective media is necessary for isolation from faeces, e.g. Skirrow's media with vancomycin, polymyxin & trimethoprim. • Incubation for 24-48 hrs at 43oC under microaerophilic conditions. • Colonies look like spreading fluid droplets. • Identification is done by Gram-film appearance, motility, growth temp. requirements 43oC • C. jejuni & C. coli : sensitive to erythromycin & nalidixic acid.
  • 143. HELICOBACTER HELICOBACTER PYLORI • Spiral-shaped, Gram negative rod, produce urease, has multiple flagella at one pole • Found closely associated with gastric mucosa & is associated with antral gastritis, gastric & duodenal (peptic) ulcer dis. & gastric carcinoma. • It differs in several important biochemical characteristics from campylobacter spp & does not grow at 43oC. Growth characteristics • Oxidase & catalase positive, motile
  • 144. HELICOBACTER Pathogenesis • Grow optimally at pH 6 -7 but not at pH of gastric lumen • Found deep in the mucus near the epithelial surface with pH 7.4 • Produce protease that modifies the gastric mucus • Produce urease –yield ammonia which buffers acid • Motility helps it to find its way to the epithelial surface • Destruction of the lumen & glandular atrophy • Toxins, LPS & ammonia directly damage the cells
  • 145. HELICOBACTER Epidemiology • Is present in the gastric mucosa of 20% in persons <30 years, but in 40-60% of persons age 60 years • Developing countries: prevalence about 80% in adults • Person-to-person transmission is likely Diagnosis • Gastric biopsy used for histology used for culture • Culture – grows in 3-6 days • Grows optimally at pH 6.0 -7.0 in Skirrow’s medium • Smear: stained with Giemsa or silver stain • Serum Ab test • Special tests: Rapid tests to detect urease activity
  • 146. HELICOBACTER Treatment Triple therapy with: • Metronidazole and either • 146Bismuth subsalicylate or Bismuth subcitrate plus • Amoxicillin or tetracycline - for 14 days eradicates H. pylori in 70-95% of patients. • Proton pump inhibitors inhibit H. pylori are urease inhibitors
  • 147. Bordetella Bordetella • Several spp of the genus cause human infections, • B. pertussis is the etiologic agent of whooping cough • B. parapertussis & B. bronchiseptica cause mild forms of whooping cough in humans. Bordetella pertussis • It inhabits the human respiratory tract, usually associated with acute disease Morphology: • Short, gram-negative bacilli • Fresh isolates are capsulated
  • 148. BORDETELLA PERTUSSIS Cultural characters: • Special enriched media required for primary isolation. • The common media - charcoal blood agar & bordet-gengou medium - made selective by the addition of penicillin or cephalexin • Growth occurs after 3-5 days of incubation in a moist aerobic atmosphere at 35oC. • Colonies are greyish-white with a shiny convex surface; "mercury drops" appearance. • Charcoal blood agar is mainly composed of beef extract, charcoal, starch, nicotinic acid, agar & blood. • Bordet-gengou medium contains 30% blood, potato extract, glycerol agar.
  • 149. B. pertussis • Bordetella pertussis, the agent of pertussis or whooping cough. Gram stain. (CDC)
  • 150. B. pertussis Antigenic structure: Virulence factors of pertussis a. Pili:- permit the adherence of B. pertussis to the ciliated epithelium of the URT b. Pertussis toxin - promotes phagocytosis. – The filamentous haemagglutinin mediates adhesion to ciliated epithelial cells. – Adenyl cyclase toxin, dermonecrotic toxin, haemolysin - synthesized & excreted by virulent strain – Tracheal cytotoxin inhibits DNA synthesis in ciliated cells c. LPS in the cell wall may also be important in causing damage to the epithelial cells of the URT
  • 151. B. pertussis Pathogenicity: • B. pertussis cause whooping cough, a highly contagious acute upper respiratory disease of children. • Infection occurs by droplets from early cases • Incubation period: 7-10 days. Stages • The organism adheres to and multiplies rapidly on the epithelial surface of the trachea & bronchi and interfere with ciliary action. • The bacteria liberate the toxins & substances that irritate surface cells, causing cough & marked lymphocytosis. • The most important symptom is cough, which is intermittent with paroxysmal attacks accompanied by a whoop & is followed by vomiting
  • 152. WHOOPING COUGH • The blood is not invaded. • Complication: bronchopneumonia, subconjunctival or cerebral hemorrhage due to paroxysms of severe cough. • Recovery is followed by long lasting immunity. Diagnosis: Specimens: Nasopharyngeal swabs or cough droplets • On BA the organism grows slowly (3-6 days) to form pinpoint colon 1. Isolation of organism: positive during the 1st week only – Collected mucus or droplets are cultured on charcoal blood agar or Bordet-Gengou media, incubated in humid atm for up to 5 days – Colonies that arise are identified by morphology, immunofluorescence staining or by slide agglutination with specific antisera
  • 153. WHOOPING COUGH 2. Direct immunofluorescence: • used to identify the organism in a smear from the nasopharyngeal swab. 3. Serologic detection of antibodies: • Abs start to appear 3 weeks after onset of symptoms. – CF & agglutination tests are used. – A rising titre should be detected. Prophylaxis: • A heat killed vaccine prepared from capsulated strains of B. pertussis is given to children during the 1st yr of life in combination with diphtheria and tetanus toxoida, i.e. as DPT vaccine. Treatment: • Antibiotics: erythromycin is effective if given early
  • 154. BRUCELLA • Predominantly infect domestic animals, from which infection may be transmitted to man causing brucellosis (undulant or malta fever). • Brucella spp are highly infectious. Spp: 6 spp currently recognized in the genus. 4 main spp, each with a number of biotypes, of concern. - Brucella abortus causing abortion of cattle. - B. melitensis causing infection in goats & sheep - B. suis causing infection in pigs. - B. canis (in dogs), rare • Some of the sub types are associated with a particular geographical location.
  • 155. BRUCELLA Habitat: • Chronic infection in domestic animals. Morphology: • Short, slender, pleomorphic, gram-negative bacilli, non motile & non-spore forming. Cultural characters: • Growth on enriched medium such as glucose serum or liver infusion broth or agar; • small transparent colonies develop after 2-3 days at 37oC in aerobic conditions; • 5-10% CO2 is required for the growth of B. abortus.
  • 156. BRUCELLA Biochemical activities: • Brucella does not ferment any sugar (doesn’t produce detectable amounts of either acid or gas) • Indole negative, turns milk alkaline, • Catalase and oxidase are positive, • Some biotypes produce H2S gas • Some are susceptible to growth-inhibitory effect of the dyes, basic fuchsin & thionine. Antigenic Structure: • They all possess 2 antigens: A and M • A is dominant in B. abortus, M in B. melitensis, • A & M are almost equal in B. suis. • In addition, a superficial L Ag (OMP Ag) similar to the virulence (Vi) antigen of salmonella are present.
  • 157. BRUCELLA Virulence factors: • No toxins, hemolysins or cell wall constituents known to play a role in the pathogenesis of disease • Rather the ability of the organism to survive within the host phagocyte & to inhibit neutrophil degranulation is a major disease causing factor. Brucellosis or Undulant fever • The disease is characterized by bouts of fever that remain for 3-4 weeks alternating with afebrile period of a similar duration, chills, sweating, headache, muscle pain, weight loss • The disease run a prolonged course accompanied with profuse sweating, headache, joint & muscle pains.
  • 158. BRUCELLA Route of infection: • The common routes of infection in humans are; 1. Intestinal tract (ingestion of infected milk) 2. Mucous membrane (droplets) 3. Skin (contact with infected tissues of animals) - Organism enters through abrasions in the skin or by inhalation. • Lymphatic dissemination of the bacteria - present in the blood stream during febrile period. • As macrophages die, brucellae are released into the blood stream & establish localised infection in the liver, spleen, kidneys, bone marrow
  • 159. BRUCELLA • Mammary glands in humans & animals infected, brucellae are shed into breast milk • Placental & fetal tissues infected in animals - abortion, but this is not a human phenomenon. • The reason is due to erythritol in the animal placenta; the sugar that enhances the growth of brucellae. Diagnosis of brucellosis (undulant fever ) • Specimens: blood, biopsy (bone marrow, liver), sera for serology 1. Blood culture: • Isolation of the organism from the blood by repeated blood cultures on liver-infusion broth incubated in 5-10% CO2.
  • 160. BRUCELLA • Subcultures are done on liver-infusion agar. • Blood cultures should not be discarded before 4 weeks incubation • Isolated organisms are typed by H2S production, dye inhibition & serologically identified by specific antisera. 2. Serological diagnosis: • Detection of Abs in the serum of the pts; these appear 7-10 days after the beginning of the fever. • IgM level rise during the 1st week of illness. • IgG levels rise about 3 weeks after onset of acute disease & remain high during chronic disease. • IgA levels parallel to the IgG levels.
  • 161. BRUCELLA a. Brucella agglutination test - A dilution of pt sera should used (up to 1/1280). A titre of 1/100 -1/200 may be considered of diagnostic significance. - A second serum sample should be tested to detect a rising titre b. Blocking antibodies: • Detected by the Coomb's antiglobulin test. These Abs appear during the subacute stage of infection, tend to persist for many years. c. Other serological tests e.g. CFT, RIA & ELISA. 3. Skin tests: ‘Brucellin test’: an intradermal skin test • A protein extract of brucella is used for ID injection. • Induration appears within 48-72hrs.
  • 162. BRUCELLA Treatment: – Streptomycin, tetracyclines & ampicillin are effective. Treatment must be prolonged due to the chronicity of the disease & intracellular survival of the organism. Prophylaxis: 1. Live attenuated vaccine used for cattle. • No vaccine is available for humans. 2. Control of milk supply by pasteurization.
  • 163. Haemophilus Important properties • Haemophilus organisms are small, some times pleomorphic, and gram-negative bacilli. • Haemophilus influenzae is the species most commonly associated with disease. • However, Haemophilus ducreyi and Haemophilus aegypticus are less frequently isolated human pathogens.
  • 164. HAEMOPHILUS INFLUENZAE • Cause respiratory disease complications (bronchitis, pneumonia, otitis media & sinusitis) in pts with viral influenza • Present in the nasopharynx of approximately 75% of healthy children and adults, hasn’t been detected in other animal. • Usually the non-encapsulated strains are harbored as normal flora, but a minority of healthy individuals (3 -7%) intermittently harbor H. influenzae type b encapsulated strains in the URT. • Pharyngeal carriage of Hib is important in the transmission of the bacterium.
  • 165. Morphology: • Gram- negative coccobacilli; non-sporing, non motile, usually capsulated. Cultural characters: • Facultative anaerobes, require blood containing media for their growth such as blood or chocolate agar. • Most species grow poorly in absence of O2 & growth is enhanced in atmosphere with added CO2. • Enriched media are necessary because Haemophilus spp need one or both of 2 growth factors: 1. Heat stable X factor - haemin or some other iron containing porphyrin 2. Heat labile V factor - di or tri-phosphopyridine nucleotide
  • 166. Antigenic structure: • Smooth capsulated strains can be classified into 6 serotypes (a, b, c, d, e, f) depending on the capsular polysaccharide. • H. influenzae type b is the most antigenic. Possess poly rabitol capsule (PRB) • Pili and non-pilus adhesions mediate colonization of the oropharynx with H. influenzae. • Cell wall components of the bacteria impair ciliary function leading to damage of the respiratory epithelial and endothelial cells and can enter the blood stream.
  • 167. Pathogenicity: • Non capsulated strains are mainly responsible for exacerbations of chronic bronchitis . • Capsulated strains (mainly type b) cause various infections mainly in children aged from 2 months to 3 yrs • H.influenzae is responsible for meningitis, epiglottitis, cellulites, arthritis, otitis media, sinusitis, lower respiratory tract disease and conjunctivitis.
  • 168. Diagnosis of H. influenzae infections:- Specimens:- pus, sputum, CSF 1. Smears are gram stained. When present in large numbers in specimen, organism is directly detected by immunofluorescence or capsule swelling test. 2. Detection of H. influenzae polysaccharide in CSF (by counter - immunoelectrophoresis). 3. Culture:- specimens are inoculated on chocolate agar. Colonies are identified by their morphology, inability to grow except on blood containing media, i.e. assays in detection of X & V factors and serologically typed with specific antisera.
  • 169. HAEMOPHILUS DUCREYI • Causes chancroid / soft sore - an ulcer on the external genitalia - STD. • The chancre is soft, unlike the hard chancre of syphilis. • Draining lymph nodes are tender & enlarged. Diagnosis: • Smears made from lesions or material aspirated from lymph nodes, show G -ve coccobacilli that may be intracellular. • It is possible to grow the organism with difficulty on blood containing media (chocolate agar). Treatment: • Sulphonamides & streptomycin - used successfully in treating the infection.
  • 170. SPIROCHETES • Large heterogenous group of spiral shaped, motile organisms Habitat: • Most are free living & non pathogenic, but few cause important human diseases. Morphology: • Spirochetes have unique helical structure: – Central protoplasmic cylinder bounded by the cytoplasmic membrane – Cell wall of similar structure to that of gram negative bacteria. • The axial filaments regarded as internal flagella
  • 171. Consist of three genera that are medically important 1. Treponema causes syphilis, yaws & pinta. 2. Borrelia causes relapsing fever & Lyme dis. 3. Leptospira causes leptospirosis (Weil's dis). • The genus treponema includes few pathogenic members. Treponema • Treponema pallidum is the most important & is the causative organisms of syphilis. • Many commensal spp occur in the mouth & genitalia. Morphology: • Slender, with spiral coils regularly spaced 1um apart • They are actively motile by means of an axial filament
  • 172. Treponema pallidum • The treponemes replicate by transverse fission, the cells may remain joined to each other. • Treponema spp are not stained with Gram, but can be seen by dark-ground microscopy in unstained preparations, fluorescent- labeled Ab, or silver stain is needed to demonstrate the spiral morphology.
  • 173. Disease Syphilis 1. Primary syphilis: • The bacteria enter the body through tiny breaks in the skin & mucous membranes. • The treponemes enter the lymphatics, the regional lymph nodes become involved, and bacteraemia occurs. • Chancre develops, at the site of inoculation, 6-12 wks after exposure to infection as a papule on the genitalia which ulcerates, not painful, which heals spontaneously. 2. Secondary syphilis:- • Lesions occur 6-12 weeks after the appearance of the chancre & are characterized by generalized manifestations, e.g. skin rash.
  • 174. • T. pallidum is found in large numbers in the lesions of both primary & secondary stages and highly infectious. • About 25% of patients are cured, 25% progress to the tertiary stage 3. Tertiary syphilis:- • Cellular immune response to T. pallidum & its metabolic products. • Characterized by appearance of gummata in the internal organs 5-40 yrs after initial infection, if not treated. • CNS involvement as manifested by tabes dorsalis & paralysis. • Cardiovascular lesions causing aortic aneurism are common
  • 175. Syphilis Lab Diagnosis: I. Detection of sphirochaetes in the lesion – A wet mount is prepared from exudate collected from the chancre in primary stages & from the skin eruptions & mucous patches in secondary stages. a. Dark-ground microscope shows living motile spirochaetes with a characteristic slow movement & angulation. b. Direct immunofluorescence using fluorscein labeled anti-treponema Abs. II. Serologic diagnosis (STS): These are either treponemal or non-treponemal antigens.
  • 176. BORRELIA • Many members of the genus are commensals. • Pathogenic borrelia cause relapsing fever & lyme disease. • Lice or ticks become infected by feeding on patient's or rodent's blood during the bacteraemia stage. Morphology: • Large spirals with irregular coils. • The coils are irregularly spaced 2-4um apart. • Motility is by both a rotating & a twisting motion. • They are stained with ordinary stains & are gram- negative, also stained with blood stain as Giemsa or Wright's stain.
  • 177. BORRELIA Cultural characters: • They can be cultured in the fluid media containing blood, serum or tissue. Antigenic structure: • Borreliae are antigenically variable • B. recurrentis show antigenic variation in vivo. Borreliae isolated from different hosts or vectors are designated as strains of B. recurrentis. Relapsing Fever • A disease characterized by repeated bouts of fever alternating with periods of apyrexia. • It is caused by B. recurrentis and its variants.
  • 178. Relapsing Fever • Epidemic relapsing fever is transmitted by lice while endemic RF is transmitted by ticks. Rodents are reservoir for the organism • Borrelia multiplies in the blood of the insect & infection is transmitted by their bite or by rubbing crushed lice or ticks into bite wounds. • After an IP of 3-10 days, there is sudden onset of fever which lasts for about 4 days followed by a febrile period of 3-10 days when the pt develops another bout of fever. • The organism is found in large numbers in the blood during the febrile stage. • Abs against Borrelia appear during the febrile stage; these agglutinate & destroy the organism and the attack is terminated. • Antigenic variants of Borrelia emerge, cause the relapse.
  • 179. Relapsing Fever Diagnosis: • Blood is obtained during the rise in temperature for smear & animal inoculation. 1. During the febrile stage: Blood films stained with leishman or Giemsa stain reveal large numbers of loosely coiled spirochetes among red cells. 2. During the afebrile stage: The organism is scanty in the blood & blood films are negative. • Diagnosis is done by injecting white mice IP with 1-2ml patient's blood. After 2-4 days, films from tail blood are stained & examined for presence of borrelia. • The animal acts as in vivo enrichment medium.
  • 180. Relapsing Fever 3. Serological diagnosis: • Complement fixation test (CFT) is used patients may have positive VDRL. Treatment: • by penicillin, tetracyclines, erythromycin & chloramphenicol. • Jarisch Herxheimer reaction is produced following antibiotic treatment.
  • 181. Mycobacteria • Mycobacteria are rod shaped, aerobic bacteria that do not form spores. • Several members produce disease in man and animals while others are saprophytes. The commoner spp are classified into: 1. The typical tubercle bacilli: M. tuberculosis, M. bovis 2. The atypical or environmental mycobacteria (opportunistic pathogens) - found in water, soil, animals and man, without evidences of disease. 3. M. leprae.
  • 182. Mycobacterium tuberculosis Morphology: • Thin straight or slightly curved rods. • They can not be stained by simple stains due to their high lipid content including mycolic acids (long chains fatty acids), waxes and phosphatides. • In the cell, the lipids are largely bound to proteins & polysaccharides. • When stained by Ziehl-Neelsen stain, they appear as thin pink rods arranged singly or in small groups. • Once stained, they resist decolouriziation with 20% H2SO4 & alcohol.
  • 183. Cultural characters: • Mycobacteria are strictly aerobes. • They grow on egg - enriched media such as Lowenstein-Jensen (LJ) medium containing a selective agent (malachite green), so it is a selective as well as enriched medium. • They grow very slowly; no growth appears before 2-4 weeks incubation at 37oC. • The growth on LJ medium is irregular, dry and yellowish in colour.
  • 184. Animal pathogenicity: • Both M. tuberculosis & M. bovis are pathogenic to guinea pigs. • When injected sc, a local nodule develops and ulcerates within 4-6 weeks. • It is associated with enlargement of the draining L nodes. • Rabbits are more susceptible to M. bovis, which causes generalized fatal infection than M. tuberculosis, which causes mild local lesions. • The disease can affect any organ of the body. • M. bovis is transmitted by ingestion of milk from infected cattle and cause intestinal tuberculosis.
  • 185. Pathogenesis: • M. tuberculosis produces no recognized toxins. • The disease results from the multiplication and local invasion at the site of infection. • The organism is capable of multiplying intracellularly stimulating CMI & hypersensitivity which leads to tissue damage. • The resulting pathology depends on whether the disease is a primary infection, a reinfection or reactivation. • Infection with M. tuberculosis confers on the pt 2 conditions, resistance and hypersensitivity. • Immunity & hypersensitivity are the features of CMI to TB.
  • 186. Transmission • Human TB is caused by M. tuberculosis and M. bovis. • M. tuberculosis is transmitted by droplets Diagnosis of tuberculous infections: • Diagnosis depends on detection and identification of the tubercle bacilli (TB) in, and their isolation from pathologic specimens.
  • 187. Specimen: • TB can affect every tissue in the body; thus the type of specimen for examination varies widely. • Sputum is examined for diagnosis of PTB • Urine sample for renal tuberculosis, • CSF for meningeal tuberculosis, • stools for intestinal tuberculosis, etc. • The following steps are made for detection or isolation of TB from sputum.
  • 188. Direct smears: – Specimens: stained with Ziehl-Neelsen stain. – The detection of AFB in sputum gives a fairly strong indication of PTB, but are detected only if they are present in large numbers. – The smear may be stained by auramine O and examined by the fluroescent microscope for yellow fluorescing tubercle bacilli. – Negative specimens are repeated for 3 successive days and re-examined after concentration.
  • 189. Treatment: The policy in treatment of tuberculosis requires: 1. Prolonged treatment: There is a slow response of TB treatment and it should be continued for 6-12 months (DOTs = 6-8 mo). This is because: a. Most bacilli are found intracellular b. The caseous material interfere with the drug. c. In chronic lesions TB bacilli are not dividing, i.e. "metabolically inactive", hence resistant to drugs,
  • 190. 2. Combination of drugs due to: a. The prolonged course of treatment needed, which may lead to toxicity, and b. The rapid emergence of resistant strains. – Combination of drugs should be used to reduce toxicity and resistance. – The drug of choice are isoniazide (INH), rifampicin, streptomycin, para-amino-salicylic acid & ethambutol. Prevention: A.Public health measures • Early Dx of cases and their treatment until they become non-infectious. • Control of infection from milk by pasteurization of milk.
  • 191. B. Vaccination: • A live-attenuated vaccine – BCG commonly used. • It is prepared from bovine strain with a fixed very low virulence. • This attenuated strain was obtained by repeated subculture of the organism in media containing bile. • The vaccine is given in a single dose of 0.1ml containing 1-2 million organisms ID in the deltoid region. The aim is to create a controlled focus which stimulates hypersensitivity and CMI against infection with both human & bovine types. • BCG is nowadays used to stimulate non specifically CMI in certain tumors.
  • 192. MYCOBACTERIUM LEPRAE • M. leprae - causes Hansen’s disease / leprosy in man, which affects mainly the mucous membrane of the nose, skin and nerve fibers. Morphology: • They are similar in size & shape to the TB bacilli. • They are acid fast, only to 5% H2SO4 which is used for decolourization. They are also alcohol fast.
  • 193. Pathogenesis • Leprosy (Hansen’s disease) is caused by M.leprae. Intracellular pathogens replicate within skin histocytes, endothelial cells, and the schwann cells of nerves. Two distinct forms of leprosy – tuberculoid and lepromatous exist.
  • 194. tuberculoid leprosy – the cell-mediated response to the organism limits its growth – very few acid-fast bacilli are seen – granulomas containing giant cells form – the lepromin skin test result is positive
  • 195. lepromatous leprosy – the cell – mediated response to the organism is poor – the skin and mucus membrane lesions contain large numbers of organisms – foamy histocytes rather than granulomas are found – the lepromin skin test result is negative. – Note that in lepromatous leprosy, only the cell- mediated response to M.leprae is defective
  • 196. Treatment • Dapsone with or with out rifampin is used to treat the tuberculoid form of disease • clofazimine is added for the treatment of the lepromatous form. • Therapy is given for longer period. Prevention and Control • Chemoprophylaxis with dapsone for exposed children is recommended. • Disease is controlled through the prompt recognition and treatment of infected people.
  • 197. Mycoplasma • Formerly pleuropneumonia-like organisms (PPLO) because they were first described as causing pleuropneumonia in cattle. Properties of Mycoplasma • Mycoplasma are among the smallest living mos capable of independent existence. • No rigid cell wall, but are composed of a small unit of cytoplasm enclosed in a protein - lipid membrane. Normal habitat: • Wide spread in nature being found in soil, plants and the mucous surfaces of animals. • In humans, M. hominis & U. urealyticum can be found in the lower urogenital tract, mouth and throat • M. pneumoniae can be found in the respiratory tract.
  • 198. M. pneumoniae • Causes pulmonary disease – upper respiratory illness, sore throat, ear infections, atypical pneumonia (characterized by slow onset, fever, headache, malaise, non-productive cough). • Expectorated sputum is mucoid; contains neutrophils, bacterial cell are not visible on Gram stain.
  • 199. Treatment • Mycoplasma are sensitive to tetracyclines and erythromycin. • They are resistant to penicillin & cephalosporins because mycoplasma lack cell walls and these drugs interfere with bacterial cell wall synthesis.
  • 200. Chlamydiae • Chlamydiae consists of 4 spp that cause a variety of disease including genital and RT infections. • They are non-motile & form intracellular inclusions in the host cell that can be seen by light microscope. • They reproduce in the cytoplasm of host cells and cannot survive outside the cell due to their limited metabolic capacity. • They use ATP produced by the host cell to fuel their metabolic reactions. • They possess both RNA & DNA, differentiating them from viruses • have cell walls similar in structure to G-ve bacteria.
  • 201. Chlamydiae Species of chlamydiae • Chlamydia trachomatis • Chlamydia psittaci • Chlamydia pneumoniae • Chlamydia pecorum Chlamydia trachomatis • Chlamydia trachomatis is an obligate intracellular bacterium with 15 immunotypes, as follows:
  • 202. Chlamydia trachomatis 1. A- C cause trachoma endemic in Africa, Asia) – Within the spp, there are different serotypes of C. trachomatis: A, B, Ba, C - associated with trachoma, a preventable form of blindness. 2. Serotypes L1, L2, L3 – Associated with LGV - STI that results in inflammation of genital tract LNs - genital ulcer in tropical countries. 3. Serotypes D-K: associated with genital tract infection (urethritis,cervicitis, epididymitis, proctitis, endometritis ,Inclusion conjunctivitis )
  • 203. Chlamydia pneumoniae • Human pathogen that causes respiratory tract infection. • The genetic make-up of C. pneumoniae varies from the other 3 spp of chlamydia. There is less than 10% similarity between C. pneumoniae and other spp • Pneumonia caused by C. pneumoniae is sometimes referred to as walking pneumonia.
  • 204. Chlamydia psittaci • Ubiquitous among spp of birds and is common in domestic mammals. • Infection in birds usually involves the gastrointestinal tract, and is shed in feces. • Humans can become infected through exposure to infected birds (psittacosis). • Cats can develop respiratory tract infection (feline pneumonitis) and in cattle, infection may result in abortion (bovine abortion).
  • 205. Rickettsiae • obligate intracellular bacteria transmitted to humans by arthropods vectors • e.g. lice, ticks & fleas, that play important roles in their life cycles. • They share some antigens proteins with other spp • C. burnetii :– rickettsia- like bacterium that causes systemic diseases. • Pathogenic rickettsiae: typhus, spotted fever and scrub typhus group.
  • 206. Morphology: • Rickettsiae are pleomorphic, G-ve, coccobacilli, better stained with Giemsa (appear blue) & with maccchiavello stain (appear red). • They have cell walls made up of peptidoglycans resembling those of G -ve bacteria
  • 207. Rickettsiae Pathogenesis: • Rickettsiae enter the body through the bite or feces of an infected arthropod vector. • They enter endothelial cells by induced phagocytosis, multiply intracellularly & destroying their host cells. • The bacteria invade vascular epithelial cells & become widely disseminated. • Human infection results from inhalation of dust
  • 208. Rickettsiae Basic features of ricketsiae and C. burnetii • Rickettsiae & C. burnetii resemble viruses in that they are mostly obligate parasites and are unable to survive as free living organisms. • They are about the size of the largest viruses & can be seen with the light microscope. • Unlike viruses, they contain both RNA and DNA, multiply by binary fission, have cell walls that contain muramic acid, possess enzymes, and show sensitivity to antiseptics & antibiotics.
  • 209. Rickettsiae Toxic properties: • Rickettsiae contain toxins that produce death in animals within a few hours after injection. Disease caused by Rickettsiae: • Rickettsial infections are characterized by fever, headache, malaise, skin rash & enlargement of the liver and spleen. • The rash is due to focal areas of infection that cause hyperplasia & inflammation of the vascular epithelium. the result is thrombosis & blockage of the small blood vessels.
  • 210. Rickettsial Diseases 1. Epidemic typhus: • Occurs in epidemics & is transmitted by body louse. • Initial symptoms of the disease are headache and fever 6-15 days after being exposed to R. prowazekii. • Macular rash start after 4-6 days of illness on the trunk and axillary folds & then spread to the extremities • The mental state of the patient may progress from dullness to stupor and, in very severe cases, even coma. • Prompt treatment may be life saving. • The disease is fatal especially in old age. • The Weil Felix reaction is positive with proteus OX-19.
  • 211. Rickettsial Diseases Brill-Zinsser disease • Relapse of louse-borne typhus that commonly occurs many years after the primary infection. • The syndrome is milder & of short duration than the primary disease. • Precipitating factors as those lowering the immunity may lead to reactivation of latent infection. • R. prowazekii remains sequestrated in cells of reticuloendothelial system. • Antibody titre to proteus OX-19 are absent. Such individuals are immune to a 2nd infection.
  • 212. Rickettsial Diseases 2. Murine typhus (endemic typhus): • The causative organism is R. typhi. • The clinical picture is in common with that of epidemic typhus, the disease is milder and is rarely fatal except in elderly patients. • The vector for human infection is the rat flea. Human is accidental hosts. • The disease rambles louse-borne typhus in pathogenesis, symptomatology & serology.
  • 213. Rickettsial Diseases 3. Tick-borne spotted fever • Has clinical similarities among the tick-borne rickettsioses of the spotted fever group. • The most severe is Rocky Mountain spotted fever. Causative organism is R. rickettsii. • The spotted fever resembles typhus clinically; however, unlike the rash in other rickettsial diseases, the rash of the spotted fever group usually appeared first on the extremities before spreading to the trunk. • The appearance of the rash on the pales & palms of the feet is considered diagnostic.
  • 214. Rickettsial Diseases • Vascular damage in severe cases may result in haemorrhagic rash, hypotensive shock, pulmonary edema & impairment of CNS function. • Infection with spotted fever group rickettsiae confers long lasting immunity. • Several species of ticks are the natural vectors of Rocky Mountain Spotted Fever, each prevails in a particular region. • R. rickettsii is transferred transovarially in ticks. • The Weil-Felix reaction is positive with porteus OX-19 and OX-2.
  • 215. Rickettsial Diseases 4. Rickettsial Pox: • Caused by R. akari, a mild infection transmitted by mites. • The clinical course is similar to other spotted fever group infections (fever, headache and eschar at the site where the infected mite fed). • The rash is first maculopapular but becomes vesicular. The rash resembling that of varicella. • Patients usually recover; • The disease is transmitted from animal to human by a rodent mite. • The major reservoir of rickettsial pox is the house mouse • Control of mice is best method of disease prevention
  • 216. Rickettsial Diseases 5. Scrub typhus: • It is caused by R. tsutsugamushi, and humans become infected from larvae of rodent mites called chiggers. • The disease resembles epidemic typhus clinically. • One feature is the eschar, the punched-out ulcer covered with a blackened crust that indicates the location of the mite bite. • Generalized lymphadenopathy & lymphocytosis are common. Cardiac & central involvement may be severe. • Antibody titers to proteins OX-K can be detected.
  • 217. Rickettsial Diseases: Q fever 6. Q fever • caused by Coxiella burnetii, an atypical rickettsial disease. • The bacteria are resistant to dryness, survive for months outside the host cell this may be due to endospore formation. • Human disease is acquired by the respiratory route rather than by the bite of an arthropod. • By inhalation of dust contaminated with rickettsiae from dried feces, urine or milk or from aerosols in slaughter houses. • The disease resembles influenza, non-bacterial pneumonia, hepatitis or encephalopathy rather then typhus. • There is no rash or local lesion. • The Weil-Felix test is negative, but there is a rise in titre of specific antibodies to C. burnetii detected by immunofluorescence assay. • Rarely infective endocarditis develops in Q fever.
  • 218. Rickettsial Diseases 7. Trench fever • Caused by Rochalimaa quintana, which are closely resemble Rickettsiae. • They can grow in cell-free media, grow on blood agar in 10% CO2. • Patients have fever, chills, headache, myalgia & is apparent when individuals are severely stressed & infested with large numbers of body lice.
  • 219. Rickettsial Diseases Lab diagnosis: Microscopy: • In tissue preparation, rickettsiae can be stained with Giemsa or Macchiavello stains. Culture: • Embryonated egg inoculation techniques are used. Serology: • Most rickettsial disease are usually diagnosed serologically - specific IgM Abs are produced followed in the later stages by an IgG response. • The IgG persist in the serum for several years. • Immunity against louse-borne typhus and spotted fever lasts for about one year after infection.
  • 220. Rickettsial Diseases 1. Prevention of transmission by breaking the chain of infections. a. Epidemic typhus: Delousing with insecticide. b. Murine typhus: Rat- proofing building and using rat poisons. c. Scrub typhus: Clearing from campsites the secondary jungle vegetation in which rats and mites live. d. Spotted fever: clearing of infested land, personnel prophylaxis in the form of protective clothing such as high boots, socks worn over trousers; tick repellents; and frequent removal of attached ticks. e. Rickettsial pox: Elimination of rodents and their parasites from human houses.
  • 221. Rickettsial Diseases 2. Prevention of transmission of Q fever: • By adequate pasteurization of milk. "High temp, short time" pasteurization at 71.5oC for 15 sec are adequate to destroy viable coxiella. 3. Prevention by vaccination: • Active immunization has been used with formalinized antigens prepared from the yolk sacs of infected chick embryos or from cell cultures. • These vaccines have been prepared for: – Epidemic typhus (R. prowazekii) – Rocky Mountain (R. rickettsi) – Q fever (Coxiella burnetti)