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

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Abstract
When grown under certain conditions some group D streptococci did not yield HC1 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/1. 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.