Evaluation of a clostridial alpha-toxin disk test for rapid presumptive identification of group B streptococci

An alpha-toxin disk test is described in which group B streptococci completed the hemolysis of sheep erythrocytes partially lysed by the alpha-toxin of Clostridium perfringens. The test was performed satisfactorily on the sheep blood agar primary isolation plate, as well as on pure cultures. A total of 95% of strains of pure group B streptococci tested produced positive reactions within 5 h, and all were positive after overnight incubation, with patterns of synergistic hemolysis readily distinguishable from those seen with group A streptococci. The preparation of disks is well within the scope of most clinical laboratories.