Shigella’s morphology :
- Short
- Gram negative
- Rod shaped
- Non motile
- Non sporing
- Non capsulated
- Fimbriae may present
- 0.5 micrometre X 1-3 micrometre
Culture characteristics :
- Aerobes
- Facultative anaerobes
- 37 degree C temp
- 7.4 PH
- Mckonkey agar : colour less
- Ordinary media : small, circular, convex,smooth, translucent
- DCA media : selective media
- Wilson & blair bismuth sulphite agar : no growth
Biochemical reaction :
- Catalase positive
- Oxidase negative
- MR positive
- Reduces nitrates to nitrites
Types :
- S. dysenteriae
- S.flexneri
- S. boydii
- S.sonnei
Mode of transmission :
- Sexually
- Through flies
- Contaminated food
Virulence factor :
- Endo toxin
- NO-H Ag
- Shiga toxin
- Shiga Toxin
- Inhibits protein synthesis
- Inhibits 28s subunit of 60s subunit ribosome
- Endotoxin
- Intestinal inflammation & ulceration
Clinical presentation :
- Watery diarrhea
- Anorexia
- Bloody stool
- Abdominal cramps
Pathogenicity :
| Infects the epithelial cells of villi in the large intestine |
| multiply |
| Spreading laterally to involve adjacent cell |
| Penetrate into lamina propria |
| Inflammatory reaction develops with capillary thrombosis |
| Leading to necrosis of patches of epithelium |
| Slough off |
| Ulceremia | bacteremia |
Lab diagnosis :
| specimen | Fresh stool |
| Transport media | Sach’s buffered glycerol saline |
| culture | Gram negative broth |
| Selective media | Mckonkey agar – pale translucent non lactose fermenting agar |