ENTERIC FEVER.pptx
- 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