VIOLET RED BILE AGAR (1.2 %)

Violet Red Bile Agar, a modification of MacConkeys original formulation is used for the enumeration of coli-aerogenes bacterial group. It relies on the use of the selective inhibitory components crystals violet and bile salts and the indicator system lactose, and neutral red. Thus, the growth of many unwanted organisms is suppressed, while tentative identification of sought bacteria can be made. Organisms, which rapidly attack lactose, produce purple colonies surrounded by purple halos. Non- fermenters or late lactose-fermenters produce pale colonies with greenish zones. VRBA is recommended by APHA. Violet Red Bile Agar (1.2 % Agar) is prepared, in accordance with the ISO Committee.
Selectivity of VRBA can be increased by incubation under anaerobic conditions and/ or at elevated temperature, i.e. equal to or above 42?C.

for selective isolation and enumeration of coliaerogenes bacteria in water, milk and other dairy food products