This medium was originally described by Slanetz and Bartley(1) for the enumeration of enterococci from water samples using membrane filtration.

The medium has also become useful as a direct plating medium.

Tryptose and yeast extract provide the required carbon, nitrogen and vitamins.

Glucose is a fermentable carbohydrate. The di-potassium hydrogen phosphate acts as a buffer.

Selectivity is achieved through the addition of sodium azide which is used to suppress the growth of Gram-negative organisms.

The medium contains tetrazolium chloride, which is reduced by enterococci to the insoluble red dye formazan resulting in dark red colonies of enterococci on the agar.

It should be noted that this reaction is not exclusive to enterococci and colonies should be confirmed by additional testing e.g. aesculin hydrolysis.