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

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Abstract
[long dash]A medium consisting of 0.5% Tryptone, 0,5% yeast extract, 0.2% L-arginine, 1.5% agar, 0.2% K2HPO4, 0.05% glucose, and 0.005% 2, 3, 5-triphenyl tetrazolium chloride (TTC) was developed to distinguish Streptococcus lactis from Streptococcus cremoris. S. lactis organisms, by virtue of their ability to produce ammonia from arginine, formed red colonies, while those of S. cremoris were white. Mutants of S. lactis strain 27, which lacked the ability to produce ammonia from arginine, were obtained by UV irradiation and selection on the differential medium. Mutant and wild type organisms were compared for their abilities to produce CO2 from arginine and citrulline; mutants had impaired activities with both substrates. No enzymes for arginine degradation were found in S. cremoris strain 144.