The Influence of the Growth Medium on the Demonstration of a Group D Antigen in Faecal Streptococci

SUMMARY: When grown under certain conditions some group D streptococci did not yield HCl extracts which would react serologically with group D antisera. By varying the composition of the medium, it was shown that the optimum yield of group D antigen was obtained when the organisms were grown in an unbuffered medium containing 5-10 g. glucose/l. where the ultimate pH of the culture was 4.0 to 4.2. In a buffered medium containing a low glucose concentration the final pH value of the culture remained above 6.0 and poor yields of group D antigen in the acid extract were obtained with Streptococcus faecium, S. durans, and S. bovis.