Evaluation of an improved rapid coagglutination method for the serological grouping of beta-hemolytic streptococci

Grouping of beta-hemolytic streptococci was performed with the Phadebact Streptococcus Test, a coagglutination method, and the results compared with serological grouping by the standard Lancefield precipitin method. Of 171 clinical specimens examined, 169 (98.8%) were grouped correctly by the Phadebact Test after 24 h of continuous growth in Todd-Hewitt broth. In a parallel study, 96.9% of specimens that grew after only 4 h of incubation in broth were grouped correctly by the coagglutination method. In both studies, the accuracy of the coagglutination test was increased significantly by elimination of multiple-agglutination reactions through centrifugation of cultures and utilization of the supernatant fluid in the Phadebact Test.