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  1. Primarily intestinal pathogens of vertebrates.
  2. S. typhi & S. paratyphi A - man is the only natural host.
    Animal pathogens- S. typhimurium , S. enteritidis, S. Newport, S. Dublin
  3. Three main types of diseases :
    1. Enteric fever :S. typhi, S. paratyphi A, B,C
    2. Gastroenteritis :
    3. Septicemia: S. choleraesuis
  4. Morphology :
a. GN, NS, NC bacilli, Non motile - S. gallinarum,  S. pullorum
  • Culture :
    • NA, BA
    • Sel F,  TTB, GN broth
    • Mac, DCA, XLD, Wilson & Blair
  • Biochemicals :
    • All Citrate +ve except S. typhi, S. paratyphi A
    • All aerogenic except : S. typhi. S. gallinarum
    • All produce H2S except: S. paratyphi A & S. cholerasuis
1. Antigenic structure :
O, H, Vi, F, M

a. antigen
  1. Somatic antigen, heat stable, alcohol stable polysaccharide, 67
  2. Anti-O titre <  Anti-H titre
  3. Anti O predominantly IgM
b. H antigen
  1. Flagellar antigen, heat labile, alcohol labile
  2. 2 alternative phases
  3. Phase 1: specific phase, small letters of alphabets
  4. Phase 2: non-specific phase, Arabic numerals
  5. Monophasic: S. typhi, S. paratyphi A, S. enteritidis
  6. Craigie’s tube
  7. H antigen not shared by other enterobacteriaceae
c. Vi antigen
  1. Heat labile, alcohol stable, acidic polysaccharide
  2. Only present in S. typhi, S. paratyphi C, S. dublin, Citrobacter
  3. Renders the bacterium inagglutinable by O antisera
  4. Anti-Vi ab disappear in early convalescence
  5. Complete absence of Vi ab is proven case: poor prognosis
  6. Persistence of Anti-Vi antibody: carrier
d. M antigen
  1. Loose polysaccharide slime
  2. S. paratyphi B
e. F antigen
  1. Fimbrial antigen
2. Antigenic Variations :
  1. OH → O, loss of H antigen
  2. Phase variation-H1 and H2
  3. Vi → W, loss of Vi antigen
  4. S → R ; prevented by Dorset's egg medium , lyophilization, Variation in ' O ' antigen  
3. Kauffman White Scheme for final identification
  1. Pathogenesis : Enteric Fever , IP- 1-2 wks, ID50-103-106
  2. Contaminated food and water
  3. Attach to the microvilli of ilea mucosa
  4. Penetrate the lamina propria and submucosa
  5. Phagocytized by neutrophils and macrophages
  6. Resist intracellular killing and multiply within these cells->Enter mesenteric lymph nodes, primary bacterimia
  7. Bacilli seeded in various organs and multiply->Secondary bacterimia
a. Complication :
  1. Perforation  
  2. hemorrhage
b. Laboratory Diagnosis : (% positivity)

 i. 1st week Blood culture 90%
  • Stool culture 50-60% : Widal 20%
ii. 2nd week Blood culture 75%
  • Stool culture 50-60% :  Widal 60%
iii. 3rd week Widal test 80-100%
  • Blood culture 60% :  Stool culture     50-60% 
Diagnosis of Carriers:   
  1. Epidemiological & public health importance and Screening food handlers
  2. 3 weeks to 3 months: Convalescent carriers
  3. 3 months to less than a year: Temporary carriers
  4. More than 1 year: Chronic carriers
  5. Fecal or urinary
  6. Diagnosis- Feces, bile or urine culture
  7. Sewer swab technique
  8. Detection of Vi agglutinins
Recent Advances :
TYPHIDOT =  Dot enzyme immunoassay  designed for the rapid diagnosis of typhoid fever. The presence of IgM and IgG antibodies produced by the patient against a specific antigen on the outer membrane of Salmonella typhi are detected by incubating nitrocellulose strips dotted with the specific antigen protein in the patient’s sera and control sera.

Widal test, all except one, are correct" (AIIMS Nov 09)
(A) Even one high titer is not enough for conclusive diagnosis.
(B) O antibody lasts longer and hence is not indicative of recent infection
(C) Baseline titers differ depending on the endemicity of the disease
(D) H antibody cannot differentiate between types.


Ans- B. O antibody lasts longer and hence is not indicative of recent infection

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