Use of Tetrazolium Dyes in an Agar Medium for Differentiation of Streptococcus Lactis and Streptococcus Cremoris

A medium consisting of 0.5% Tryptone, 0.5% yeast extract, 0.2% L-arginine, 1.5% agar, 0.2% K-.HPO,, 0.05% glucose, and 0.005% 2,3,5-triphenyltetrazolimn chloride (TTC) has been developed which may be used to distinguish Streptococcus lactis from Streptococcus cremoris. S. lactis organisms, by virtue of their ability to produce ammonia from arginine, formed red colonies; colonies of S. cremoris were white. The incol]ooration of tetrazolimn blue or tetrazolium red into the basal arginine medium in place of TTC produced analogous results.