Two Organisms of a Commercial Lactic Starter

Summary 1. Two cultures of streptococci were isolated from a commercial starter. These two cultures seemed to be necessary in order to reproduce acidity and flavor of the original starter. 2. One culture was evidently a strain of the Streptococcus lacticus group. It produced a high acidity in milk and but little volatile acidity. 3. The other culture seemed to correspond to organisms of the Streptococcus kefir type. It produced but little total acidity in milk and when grown with the Streptococcus lacticus culture produced considerable volatile acid. 4. Gas was observed in the original starter. This was undoubtedly due to the growth of the organism of the Streptococcus kefir type, since when grown with the Streptococcus lacticus culture there was a gas formation similar to the original starter. It was further observed that carbon dioxide was formed by the culture when grown in peptone milk. 5. Associative action between the two cultures was very noticeable. The results indicated that the Streptococcus lacticus type through its growth converted the nitrogenous material of the milk into a form more available for the Streptococcus kefir type and as a result the growth of the latter was increased. 6. The results reported represent a study of only one commercial starter. It remains to be determined whether the cultures are the same in all starters.