Demonstration of alpha and beta components of group B streptococcal protein antigen c in serum-soft agar.

Among 85 group B streptococcal cultures with protein type antigen c 56 cultures demonstrated a diffuse type of colony morphology in plain soft agar. The addition of monospecific antibodies against the protein antigen c components c alpha and c beta converted specifically the colony morphology from diffuse to compact. According to this results the serum-soft agar technique could also be used to further characterize individual cultures of group B streptococci with protein antigen c.