Violet Red Bile Agar is a medium for the enumeration of coliform organisms in food and dairy products and conforms to American Public Health Association (APHA).
Yeast extract and enzymatic digest of gelatin provides the required carbon, nitrogen and vitamins. Sodium chloride maintains the osmotic balance. The medium is made selective by the inclusion of bile salts and crystal violet to inhibit Gram-positive and non-enteric organisms. Lactose is a fermentable carbohydrate and neutral red is a pH indicator. Lactose fermenters produce red/purple colonies often surrounded by a halo of the same colour. Non lactose fermenters produce pale colonies. Selectivity can be increased by incubation at 42-44ºC.