Salmonella is a Gram-negative, rod-shaped bacterium that causes various clinical syndromes including enteritis and enteric fever. Enteric fever, caused by S. typhi and S. paratyphi, spreads through the fecal-oral route and has an incubation period of 10-14 days. It causes a prolonged fever and can lead to complications affecting the intestines, liver or other organs if left untreated. Laboratory diagnosis involves blood, stool or urine cultures and serological tests like the Widal test. Treatment consists of antibiotics while prevention relies on vaccination, identifying carriers, and improving sanitation.

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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