Description
The composition of the medium includes Tryptose as a source of nutrients, with mannitol and dextrose available as fermentable carbohydrates, the mannitol at a higher concentration in order to stimulate the growth of mannitol fermenting organisms such as Salmonella and Shigella species, at the expense of dextrose fermenting bacteria such as Proteus sp. Sodium chloride maintains osmotic equilibrium, while a phosphate buffering system controls rapid alterations in pH levels. Citrate and desoxychlate are inhibitory to gram positive bacteria including faecal streptococci and spore forming organisms, as well as to some coliforms. Proteus and Pseudomonas sp. will grow in the medium but will not overgrow salmonellae and shigellae in the enrichment incubation period.