Single Broth for the Differentiation of Streptococcus lactis from Streptococcus cremoris

Abstract

A procedure for the differentiation of S. lactis species from S. cremoris, utilizes decarboxylase base broth (Difco, 0872) containing brom-cresol purple indicator and fortified with 0.5% L-arginine. The test is based on the principal that S. lactis species will decarboxylate arginine, whereas S. cremoris species will not. L-arginine decarboxylate broth is inoculated at the 2% level with a 16-18 hr. skimmilk culture and is incubated at 30oC for 48 hrs. All of the 34 S. cremoris strains studied yielded negative reactions, and all S. lactis (26) strains positive reactions in L-arginine decarboxylase broth.