Rapid identification of group A, B, C and G beta-haemolytic Streptococci by a modification of the co-agglutination technique. Comparison of results obtained by co-agglutination, fluorescent antibody test, counterimmunoelectrophoresis, and precipitin technique.

A rapid modification of the co-agglutination (COA) technique for grouping A, B, C and G beta-haemolytic streptococci was developed. The results are obtained within three hours after inoculation from primary plates of 0.5 ml broth. This method was compared to the fluorescent antibody test (FA) and counterimmunoelectrophoresis (CIE), two other rapid methods available for serological grouping of streptococci. Of 71 recently isolated streptococcal strains from clinical sources, 70 were correctly grouped in COA, 63 in FA and 68 in CIE. With commercial reagents COA compared favourably in accuracy to the other methods and can be recommended for routine serological grouping of beta-haemolytic streptococci in the clinical laboratory.