Grouping of beta-haemolytic streptococci with group-specific antibodies absorbed to staphylococcal protein A

A total of 245 isolates of beta-haemolytic streptococci was grouped by the counter current immunoelectrophoresis method and by co-agglutination with antibody-coated staphylococci. Co-agglutination was found to be simple and accurate, and many commercially available grouping sera were suitable for use in this test, though some of them had to be absorbed to remove cross-reactions.