THE OCCURRENCE OF TWO M ANTIGENS IN CERTAIN GROUP A STREPTOCOCCI RELATED TO TYPE 14

A strain of Group A streptococcus previously considered to belong to Type 14 was shown to have two immunologically distinct M antigens, designated Type 14 and Type 51. Most strains having the Type 14 M antigen were found to have also the Type 51 M antigen, and are considered to belong to Type 14–51. Four strains had the Type 51 M antigen without the Type 14 M antigen and one strain had the Type 14 M antigen without the Type 51 M antigen.

The failure of a variant to produce the known M antigen of the parent strain does not necessarily mean that the strain is M^-, because a second M antigen may be present as was the case in several strains described here.