Typing Group a Hemolytic Streptococci

Two methods of typing group A hemolytic streptococci have been described: slide agglutination and anti-M precipitin tests. The first, developed by Griffith (1), is more extensively used. I t has the distinct advantages of requiring small amounts of serum and culture, and of a quick reaction time when all conditions are favorable. I t has certain disadvantages: The granular growth of some strains of streptococci is so marked that much subculturing is necessary before they are suitable for testing, and many days or weeks may elapse before the final result is available. Cross reactions are not uncommon, and make it impossible to differentiate certain types unless specially prepared sera are used which have been absorbed with regard to the antigenic relationships among types. This is due, in part, to the presence in group A streptococci of two antigens related to type specificity, so called M and T, which in a given microorganism do not always correspond (2, 3). Antibodies for one or both of these antigens have been used for the identification of types by the agglutination method. I t is no~v evident that several types contain common or closely related T antigens, but that members of each type elaborate a distinct type-specific M substance (4). So far, we have only once encountered the antigenic combination consisting of two types with a common M substance and distinct T antigens. Probably a thorough understanding of the usual antigenic make-up of each type will eventually result in more satisfactory slide agglutination tests. Anti-M precipitin typing is more precise in that a single antigen-antibody system is involved, and there is relatively little crossing among types when