Description
Wilson Blair Agar Base, formulated by Wilson and Blair is recommended for isolating Salmonella species especially Salmonella Typhi from clinical specimens. The selective reagent formulation is a modification of the bismuth sulphite reagent described by Hajna and Perry. Wilson Blair Agar Base is particularly valuable for the isolation of S. Typhi. The medium is highly selective for Salmonellae, being inhibitory to coliforms, Proteus and Shigella; occasional strains of coliforms grow to form dull green or brown colonies, but without a surrounding metallic sheen. The medium is also suitable for the isolation of lactose fermenting strains of Salmonellae (which cannot be differentiated on lactose containing differential media) since lactose is not the fermentable substrate used in this medium. Peptone special and beef extract provide nitrogenous, carbonaceous compounds and other growth nutrients. Brilliant green dye inhibits all gram-positive bacteria. Dextrose is a fermentable carbohydrate. Ferrous sulphate aids in H2S production. Bismuth is a heavy metal, which is inhibitory to most gram-negative enteric bacilli other than Salmonella. Ferrous sulphate is reduced by Salmonella species in presence of bismuth sulphite and dextrose to form iron sulphide, indicated by black coloured colonies. Disodium hydrogen phosphate buffers the medium well. Sodium chloride balances the osmotic equilibrium.contaminated water, food, or by person-to-person contact (with inadequate attention to personal hygiene).
