Basal medium for selective isolation of Salmonella non typhi and paratyphi.
X.L.T. 4 Agar, complete with Tergitol 4 (X.L.T. 4 supplement), is a medium for isolation and differentiation of enteric pathogens. Differentiation of Salmonella from other microorganisms is based on fermentation of xylose, lactose and sucrose, decarboxylation of lysine, and the production of hydrogen sulphide. Salmonella colonies, H2S positive, appear pink to red with black center; colonies of H2S negative Salmonella appear pinkish-yellow. Citrobacter grows with yellow colonies. Proteus, Pseudomonas, Providencia, Yersinia are inhibited. The diagnosis of Salmonella is confirmed with biochemical and immunological methods.