Detection of receptors for the Fc region of IgG on streptococci.

A semi-quantitative absorption test to measure Fc-reactive proteins on the surface of streptococci is described. The ability of bacteria to remove intact IgG in the presence of an equimolar amount of F(ab')2 fragments was used to identify streptococci with Fc-reactive proteins on their surface. This method was found to be more objective, reproducible and quantitative than the hemagglutination and 125I-labeled IgG binding methods currently in use. Methods for detection of secreted Fc-reactive materials with protein A-like reactivity are also described.