The Serological Grouping of Streptococcus equinus

SUMMARY: Streptococci isolated from horse faeces and corresponding to the description of Streptococcus equinus Andrewes & Horder (1906) were found to belong to the serological group D. The group D antigen was produced by all the strains examined, but was not always extractable from whole organisms by HCI or formamide; broken organisms, however, always gave group D antigen. Collections of S. equinus and S. bovis strains were found to be physiologically similar, but distinguishable.