S.typhoid And S.paratyphoid Flashcards
Classification
Family: Enterobacteriaceae
Genus: Salmonella
Species: typhi and paratyphi
Infective dose: 10^5 to 10^8
Morphology
Gram negative rod
Motile (Petrichious flagella)
Sometime capsulated
Growth characteristics
Found normally in the SI and LI
Facultatively anaerobic
Non-fastidious
Antigenic structure
Somatic O antigens H antigen (flagellate) Vi antigen (capsular) includes: - F antigen (fimbrial) - M antigen - R antigen RFM antigen
Virulence factors
> Endotoxin
> Capsule (for S.typhi and some strains of S.paratyphi)
> Adhesins- both fimbrial and nonfimbrial
> Type III secretion systems and effector molecules- 2 different systems may be found:
- one which promotes entry into intestinal epithelial cells
- one which promotes survival in macrophages
> Flagella- help bacteria to move through intestinal mucous
> Enterotoxins- may be involved in gastroenteritis
> Iron capturing ability
Disease
Typhoid fever
Enteric fevers
Microbiological diagnosis
Culture:
Blood agar plate: for specimens from normally sterile sites
Enrichment broth (GN, Selenite)
Differential medium (Mac Conkey’s, EMB agar): lactose-negative colonies
Selective medium (SS agar): colorless colonies with Black center
Biochemical tests Motile Do not ferment lactose Ferment glucose Urease negative
Salmonella typhi is very hard to isolate from culture, mainly from serum, using serological tests
Serologic test for identification:
Rapid slide agglutination test
Serologic tests for diagnosis:
Tube dilution agglutination test (Widal test)
To > 1:100
Th > 1:200
Treatment and prevention
Ampicillin
Trimethoprim-sulfamethoxazole
Third generation cephalosporin
Problem: drug resistance transmitted by plasmids
Antimicrobial susceptibility tests