Shigella

lab diagnosis of Shigella sp.

1. Shigella spp. Lab 7 Prepared by Samira Fattah Assis. Lec. College of health sciences-HMU

2. General character : - Short rods Gram-negative Non-motile Non-encapsulated facultative anaerobic Non-lactose fermenting

3. Specimen: fresh stool. Rectal swab. Serum Laboratory diagnosis

4. Microscopy: Microscopic examination is a gram negative bacilli.

5. On culture media

6. On MacConkey agar Shigellae form non-lactose fermenting  pale colored or colorless and transparent colonies 

7. On EMB agar Surface of EMB agar plates illustrating a mixed culture of E. coli (green sheen colonies) and Shigella species. Most Shigella species do not ferment lactose and, thus produce nonpigmented , semitranslucent colonies on EMB agar. 

8. On SS agar Colonies are transparent, translucent or opaque and usually smooth (non lactose fermenting).

9. On xylose lysine deoxycholate agar Shigella  growth on XLD is transparent and the same color as the medium (red).  

10. Motility test Shigella is non motile the growth of organism spreads out in only one direction, and there is a sharply differentiated edge between this growth and the agar.

11. Biochemical test Oxidase test Cytochrome oxidase negative . Catalase test positive   reaction

12. Biochemical test U rease - ve H 2 S - ve . lactose - ve Citrate - ve

13. API Test API 20E result for shigella

14. Serologic diagnosis Serologic examination with polyvalent and monovalent anti-sera For serogrouping and serotyping. It is not used to diagnose shigella infection,it is for conformation.

15. serotyping Shigella species are classified to four serogroups: Serogroup A : Shigella dysenteriae (12 serotypes) Serogroup B : Shigella flexneri (6 serotypes) Serogroup C : Shigella boydii (23 serotypes) Serogroup D : Shigella sonnei (1 serotype)