Salmonella typhi and Salmonella paratyphi cause enteric fever, also known as typhoid fever, characterized by fever, headache and abdominal discomfort. The bacteria are transmitted via contaminated food and water. Diagnosis involves blood culture early in infection or feces/urine culture later. The bacteria are identified through cultural characteristics like growth patterns and biochemical reactions. Treatment is typically with ciprofloxacin or other antibiotics. Prevention relies on sanitary food handling, clean water and vaccination.

1. ENTERIC FEVER
Sabnam Kayastha
Diagnostic Bacteriology
B. Sc. MM 6th semester

2. INTRODUCTION
• Enteric fever is caused by Salmonella typhi and Salmonella paratyphi
subtypes, also known as typhoid fever.
• Enteric fever is an acute illness characterized by fever, headache and
abdominal discomfort.
• Non typhoidal Salmonella causes food poisoning, gastroenteritis.
• Humans are the only source of this infection and the spread is from
person to person via contaminated food and water.

3. ETIOLOGY
• Salmonella typhi and Salmonella paratyphi A, B and C are the
causative agent of enteric fever.
• They are member of enterobacteriaceae family, Gram negative bacilli,
non sporing, non capsulated and generally motile.

4. VIRULANCE FACTORS
Salmonella has three types of antigen:
1. O-antigen (somatic):
• Present in the body of bacteria.
• It is endotoxin and provides antigenic variation.
2. H-antigen (flagellar):
• Present in flagella of bacteria.
• Provides antigenic variation and motility.
3. Vi-antigen (envelope)
• It is the superficial of the somatic antigen.
• Polysaccharide capsule surrounds the O antigen,
thus protecting the bacteria from an antibody
attack on the O antigen.
• This aids in resistance and compliment.

5. CLASSIFICATION
• Kauffmann and white
classification scheme is a
system that classifies the
genus of Salmonella into
serotypes based on their
surface antigen, O groups.
• Within each O groups different
serotypes are distinguished by
their H antigen(flagellar).

6. MODE OF INFECTION
• Contaminated food and meat
• Contaminated water supply

7. PATHOGENESIS

8. LAB DIAGNOSIS
1. Specimen collection
• Blood: first 10days and during 3rd weeks. 5-10ml venomous blood is collected
aseptically, inoculated in 50-100ml broth and incubated at 37’c for 24hrs.
• Feces: during 2nd and 3rd week.
• Urine: 3rd week. (not as useful as blood culture)
• Bone marrow: in case of chronic salmonellosis.

10. CULTURAL CHARACTERISTICS
• Grows in ordinary media.
• Aerobic and facultative anaerobe.
• Optimum tempeture is 37’c.
• On Blood Agar colonies are circular, low convex, smooth, greyish white,
translucent and non hemolytic.
• On MacConkey agar colonies are non-lactose fermenter i.e. pale yellow colonies
measuring about 1-3mm in diameter.
• Salmonella Shigella agar, colonies are color less with black center due to
production of H2S.

11. Continue..
• On Deoxycholate agar colonies are colorless, non-lactose fermenter and smaller
colonies than in MA.
• Wilson and Blair bismuth sulphate medium colonies are black with metallic
sheen due to production of H2S.
• Xylose Lysine Dextrose agar, the colonies are red due to fermentation of xylose
with black center due to production of H2S.
• Selenite F broth and Tetrathionate broth is the enrichment medium for
Salmonella typhi. The fecal specimen inoculated in selenite F broth are incubated
for 6-12hrs before subculture.
• Incase of negative subculture, the process is repeated for 10days and reported as
negative.

12. FERMENTATION TESTS
Serotypes Glucose Xylose D-tartrate Mucate
S. Typhi Acid Differentiate Acid Differentiate
S. paratyphi A Acid and Gas Negative Negative Negative
S. paratyphi B Acid and Gas Acid and Gas Negative Acid and Gas
S. paratyphi C Acid and Gas Acid and Gas Acid and Gas Negative

13. BIOCHEMICAL REACTION
• Ferment: Glucose, maltose
• Non-ferment: Lactose, Sucrose
• Catalase: positive
• Oxidase: negative
• Indole: negative
• MR: positive
• Citrate: utilized except by typhi and paratyphi A.
• H2S: positive except paratyphi A
• Nitrate reduction test positive.
• TSI: Alkaline/acid, H2S positive in Typhi and negative in paratyphi A

14. Widal test
• The widal test is agglutination test, developed in 1896. If
the culture facilities are not available the widal test is
valuable for diagnosis.
• Titer of O antibodies:-
1:80 is suspicious in unvaccinated patients.
1:160 is strongly suggestive of infection in unvaccinated patients.
• Titer of H antibodies:-
1:40 is suspicious in unvaccinated patients.
1:160 is strongly suggestive infection.
• Titers are much higher in vaccinated individuals.
• Vi antigen for S. typhi is used to screen the carrier.

15. Drawbacks of the Widal test:
• Antibodies are absent in the early illness, may appear after 7 days.
• Antibodies may not develop due to antibiotic therapy.
• Antibody response is variable and does not correlate with the severity of the disease.
• In some patients, there is no adequate level of O-antibody titer.
Other culture method include:
• Castaneda’s method
• It is a biphasic medium used to minimize contamination.
• Clot culture
• Clot cultures are better for the isolation of bacteria.
• In this method the blood is allowed to clot and after 30 minutes, centrifuged it and remove
the clot and put in a streptokinase broth.
• The serum from the clot has lot of antibodies which the clot doesn’t have and hence useful in
investigation.

16. Treatment
• The drug of choice is Ciprofloxacin.
• Chloramphenicol is also effective, but this may have serious side
effects.
• Co-trimoxazole is also used and has less serious side effects than
Chloramphenicol.

17. Control and Prevention
• The Hygienic measure like:
• Clean water supply.
• Adequate disposal of the sewage material.
• Washing of the hands after the defecation. The best is to wash your hands
with soap at least three times.
• Take care of food handling and processing.
• Vaccination should be advised in the family with a history of enteric
fever.

18. Vaccine types

19. THANK YOU
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