enteric bacteria

1. Typhoid/ Enteric fever
Dr. Jyotsna Agarwal
Professor, Dept. Microbiology
KGMU
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• Salmonella is Gram-negative,
rod-shaped
• Facultative anaerobe in family
Enterobacteriaceae
• Motile, Non lactose fermenting
• Over 2400 serotypes
Salmonella

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 Faeco-oral transmission
 Refrigeration does not kill bacteria, Heat at
600C destroys

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Clinical Syndromes of Salmonella
Salmonellosis = Generic term for disease
Enteritis (acute gastroenteritis)
Enteric fever (prototype is typhoid fever and
less severe paratyphoid fever)
Septicemia (particularly S. choleraesuis, S. typhi,
and S. paratyphi)
Asymptomatic carriage (gall bladder is the
reservoir for Salmonella typhi)

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Enteritis( Food Poisoning)
 Most common form of salmonellosis with
foodborne outbreaks and sporadic disease
 High infectious dose (108 CFU)
 Poultry, eggs, etc. are sources of infection
 6-48h incubation period
 Nausea, vomiting, nonbloody diarrhea, fever,
cramps, myalgia and headache common
 Many species of salmonella can cause this (eg. S.
typhimurium) except S. typhi

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Pathogenesis
 Bacteria penetrates intestinal cell in
ileocaecal region
 Inflammatory response to bacterial
multiplication in the cell
 Prostaglandins secreted
 Increase in C-AMP

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Clinical Syndromes- Enteric fever
 S. typhi causes typhoid fever
S. paratyphi A, B and C cause milder form of
enteric fever called paratyphoid fever
 Infectious dose large = 106 CFU
 Fecal-oral route of transmission
 Person-to-person spread by chronic carrier
 Fecally-contaminated food or water
 Food handlers contaminate food
 10-14 day incubation period

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 Virtually non existent in developed world
 In developing countries endemic
 Typhoid more common than paratyphoid

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Pathogenesis of Enteric fever
M cells on Peyers patches
Invade intestinal lining cells
bloodstream (primary bacteremia)
Phagocytosis
Transported (R E system), continue to replicate

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Pathogenesis contd…
 Second week: re-enter bloodstream (secondary
bacteremia) endotoxemia
 Second to third week: gallbladder, secreted in
bile, re-infect intestinal tract

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 Complications: Intestinal haemorrhage,
perforation, cholecystitis
 Less commonly: Bronchopneumonia,
arthritis, osteomyelitis

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Asymptomatic Carriage
 Chronic carriage in 1-5% of cases following S.
typhi or S. paratyphi infection (Temporary
carrier>12 months shedding)
 Gall bladder usually the reservoir
 Chronic carriage with other Salmonella spp.
occurs in <<1% of cases and does not play a
role in human disease transmission
Epidemiology & Clinical Syndromes

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Early 1900- Mary Mallon

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Virulence factor
•Encapsulation , antigenic mimicry, masking
•Evasion or incapacitation of phagocytosis
• Mechanisms enabling an invading
microorganism to resist being ingested and lysed
by lysosomes
intracellular survival and multiplication
•Endotoxin

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Diagnosis of Typhoid Fever
 Clinical:
 For Lab diagnosis, specimen & diagnostic tests
according to duration of fever:
1. Blood for Culture
2. WIDAL
3. Stool culture
4. Urine culture

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Blood Culture
 In blood culture bottle
 Repeated cultures may be required
 Subculture on MacConkey medium (NLF colony)
 Clot culture- put clot in blood culture bottle, lyse it with
streptokinase in B/C bottle
 Use serum for WIDAL

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 Selective media for subculture from blood
culture bottle: MacConkey, Wilson Blair,
Tellurite blood agar
 Enrichment broth for culture of stool/urine:
Selenite F broth, Tetrathionate broth

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Serological test- WIDAL
 For detecting antibody
 Agglutination test
1. Endemic titre
2. Paired sera
 For carriers - antibody against Vi antigen
 Rapid test- Typhi dot

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Treatment, prevention & control of
salmonella infections
Enteritis:
 Antibiotics not recommended for enteritis
because prolong duration
 Control by proper preparation of poultry & eggs
Enteric fever:
 Antibiotics- Chloramphenicol, cipriflox,
Ceftriaxone
 Identify & treat carriers of S. typhi & S. paratyphi
 Vaccination can reduce risk of disease for
travellers in endemic areas

20. Salmonella vaccines
 TAB: Salmonella typhi, paratyphi A &B, killed whole
cell
 Oral Ty21-A: Live attenuated, Salmonella typhi
vaccine
 Vi capsular polysaccharide vaccine
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21. Summary- Enteric fever
 S. typhi / S. paratyphi
 Mode of spread /Pathogenesis
 Clinical features / Complications
 Laboratory diagnosis
 Treatment/vaccines
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