SHIGELLA

1.      It is gram negative.

2.      Non-motile

3.      Enteric pathogen causing bacillary dysentery

4.      It has four species

a)      Shigella dysenteriae

b)      Shigella flexneri

c)      Shigella boydii

d)      Shigella sonnei

Found in only humans intestinal tract.

It is acquired by ingesting contaminated food and water with shigellae.

1.5.1: Culture characteristics:

1.      Facultative anaerobes

2.      Catalase positive except Shigella dysenteriae

3.      Does not produce H2S

4.      On Blood Agar

5.      2-4mm in size

6.      Entire and convex

7.      On MacConkey Agar

8.      Pale colonies

9.      Non lactose fermenting

10.  Following other media are used

11.  Deoxycholate citrate agar (DCA)

12.  Salmonella Shigellae agar (SS agar)

13.  Xylose lysine Deoxycholate agar (XLD agar).(Monica2000)

Antisera are used for the identification by agglutination reaction.

1.5.2: Pathogenicity

Pathogenesis includes

1.      Bacillary dysentery

2.      Meningism and other neurological symptoms.

3.      Neurotoxins produce by shigellae type-1 which affects central nervous system.

1.5.3: Antibiotic sensitivity

Shigellae susceptible to

1.      Ampicillin

2.      Chloramphenicol

3.      Cotrimoxazole

4.      Tetracycline

5.      Nalidixic acid

6.      Fluoroquinolones (Ciprofloxacin and Ofloxacin).(Monica2000)