[Streptococcus dysgalactiae subsp. equisimilis possessing Lancefield's group A antigen].
We isolated Streptococcus dysgalactiae subsp. equisimilis with Lancefield's group A antigen from a patient in Osaka City. This clinical isolate formed beta-hemolytic large colonies on sheep blood agar, and was catalase-negative gram-positive cocci carrying Lancefield's group A antigen. Therefore, Streptococcus pyogenes and this clinical isolate could not be classified by the conventional method on the basis of Lancefield's group antigen. In addition, the rapid detection system of group A streptococci based on group A antigen detection techniques could not divide into two species. Recently, S. dysgalactiae subsp. equisimilis with Lancefield's group G antigen has been isolated from severe invasive streptococcal infection in an increasing frequency in Japan. A possibility that group A S. dysgalactiae subsp. equisimilis cause a serious infection from now on cannot be denied. Thus the discrimination of S. pyogenes from group A S. dysgalactiae subsp. equisimilis is very important. To identify beta-hemolytic streptococci, it is necessary to consider a serogrouping test as one of characteristics of streptococci, and to identify by checking biochemical tests like the PYR test.