VMC 311: Systematic Veterinary Bacteriology and Mycology (2+1)

STAINING ,CULTURAL CHARACTERS AND SLIDE AGGLUTINATION TEST

Staining

• They are Gram negative short rods or coccobacilli. With the exception of S. pullorum and S.gallinarum, all strains normally posses peritrichous flagella.

Cultural characters

• Certain chemicals like sodium selenite and tetrathionate are used to enrich the medium used for the isolation of Salmonella organisms from faecal sample. Hence, selenite broth or tetrathionate broth are used as enrichment media.
• In MacConkey agar, it produces pale, non lactose fermenting colonies.
• Most salmonellae give bright pink colonies on brilliant green agar and alkaline reaction in the medium.
• On XLD medium, the majority of Salmonella serotypes produce H₂S and have red colonies with black (H₂S) centre.
• In hektoen enteric agar it forms blue green colonies with black centers (H₂S).
• In Salmonella - Shigella agar the colonies of Salmonella appear as smooth, small and colourless. The center of the colonies may be dark if they are H₂S producers.

Biochemical properties

IMViC	- + - +
Urease	-
Lysine	+
H2S	+

Laboratory Indications

Lysine	+
H2S	+
Indole	-
Citrate	+
Malonate	-
ONPG	-
H2S reaction (with gas)	-/+

Slide agglutination test

• Smooth Salmonella culture is emulsified in a drop of 0.85% saline on a clean microscopic slide.
• A drop of antiserum is added to and mixed well with the Salmonella suspension.
• The slide is rocked gently for about 30 seconds and examined for agglutination.