Shigella spp.

Lab 7

Prepared bySamira Fattah

Assis. Lec.College of health sciences-HMU

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

Specimen:

• fresh stool.• Rectal swab.• Serum

Laboratory diagnosis

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

On culture media

On MacConkey agar

Shigellae form non-lactose

fermenting pale colored or colorless and transparent colonies

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.

On SS agar

• Colonies are transparent, translucent or opaque and usually smooth (non lactose fermenting).

On xylose lysine deoxycholate agar

Shigella growth on XLD is transparent and the same color as the medium (red).

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.

Biochemical test

• Oxidase test• Cytochrome oxidase negative.

• Catalase test• positive reaction

Biochemical test

• Urease -ve • H2S -ve.• lactose -ve• Citrate -ve

API Test

• API 20E result for shigella

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.

serotypingShigella 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)