15. shigella

MICROORGANISM

1. SHIGELLA DYSENTERIAE RATHEESH R.L

2. MORPHOLOGY An enterobacteriaceae Gram negative bacilli. Mostly non-motile N on sporing Size varies from 2-4um x 0.4 -0.6um

3. CULTURAL CHARACTERISTICS They are aerobics and facultative anaerobics Growing well in the temperature of 37 degree C and in the pH of 7.4.

4. NUTRIENT BROTH They produce mild turbidity after 24 hours of incubation.

5. NUTRIENT AGAR OR BLOOD AGAR MEDIUM Circular, smooth grayish or colorless Colonies will be formed after overnight incubation. Size of the colonies will be 2-3mm

6. MACCONKEY AGAR MEDIUM They produce colorless colonies in the medium

7. XLD(xylose lysine deoxycholate ) AGAR MEDIUM It is a selective medium and the colonies formed are red color without black centers.

8. DEOXYCHOLATE CITRATE AGAR MEDIUM It is a selective medium for shigella dysenteriae Small colorless colonies will be formed in this medium.

9. PATHOGENESIS The species of this genus causes a serious illness known as dysentery/shigellosis , which is an acute diarrheal disease characterized by passage of pus, blood or mucous through the stool. Infection mainly occurs because of the ingestion of contaminated food or water.

10. Incubation period is 12-48 hours but may vary between 1-7 days. Through the ingestion the bacilli will reaches to the large intestine of the humans. The multiplication occurs in the epithelial cells of the large intestine.

11. Then the bacteria spreads to adjacent cells and to the lamina propria (is a thin layer of loose connective tissue which lies beneath the epithelium) where the colonization occurs.

12. After the growth and multiplication, it starts to produce toxins. The lamina propria and sub mucosa develops an acute inflammatory reaction with formation of abscess on the mucosal surface along with capillary thrombosis by the production of toxins .

13. The necrosed epithelium become soft and sloughed out and causing superficial ulcers and bleeding. The toxin produced by the shigella bacteria have both enterotoxic effect and neurotoxic effect.

14. Thus their combined action leads to severe diarrhea,poly neuritis, coma and meningitis.

15. LABORATORY DIAGNOSIS Hematological investigations Bacteriological investigations Microscopic studies Culture studies Biochemical tests Slide agglutination test

16. Hematological investigations There will not be any significant changes in the blood values.

17. Microscopic studies Under the microscope the wet preparation of specimen shows large number of pus cells with degenerated nuclei, macrophages and RBC.

18. CULTURE STUDIES Feces or mucous specimens are selected for the microscopic studies. After 12-18 hours of incubation non lactose fermenting colonies will be formed in the macconkey medium.

19. Biochemical tests H2S test: negative Citrate utilization test: negative Iodole test: positive M.R test: positive Urease test: negative Motility test: negative

20. Slide agglutination test It is performed with specific antisera against the shigella dysenteriae . We can isolate the bacilli by adding the antisera over the specimen.

21. TREATMENT Tetracycline and chloramphenicol is the drug of choice against the shigella dysenteriae . The treatment should be continued for 5-7 days.