Serological grouping of streptococci by a slide coagglutination method.

A new method for the serological grouping of streptococci by coagglutination with specific antibodies absorbed to protein A-containing staphylococci has been assessed. A total of 242 strains of streptococci, including beta-haemolytic streptococci of groups A, B, C, F, and G, Streptococcus pneumoniae and Strep. faecalis were studied. All streptococci of groups A, B, C, and G, groupable by standard methods, were correctly grouped by coagglutination, although 7-3% showed varying degrees of cross-agglutination. Two beta-haemolytic strains of Strep. faecalis produced coagglutination with group C streptococcal reagent. The method appears to be quick, accurate, reproducible, and simple to perform.