Nutrition of Streptococcus lactis

Although Streptococcus lactis is the oldest known species of the genus, and one of the most common organisms encountered in the dairy industry, very little attention has been devoted to its nutritive requirements. As difficulty has been encountered in this laboratory in culturing members of this species in simplified media, an attempt was made to determine their nutritive requirements. The present study describes the cultivation of Streptococcus lactis cultures in a medium consisting of only chemically defined ingredients. CULTURES AND TECHNIQUE The cultures employed throughout the major part of this investigation con-sisted of 11 Streptococcus lactis strains from the laboratory stock culture collec-tion and 10 recently isolated strains. The 21 cultures were isolated from as many different samples of raw milk. All had been identified previously on a physiological basis as typical members of this species. Extracts of the 11 stock cultures revealed negative precipitin tests with Lancefield serological group D serum but gave strong precipitin reactions with a species-specifi