Identification of group a streptococci by reverse passive hemagglutination.

A method for preparing sensitized human O erythrocytes with specific antibody is reported. Whole sera or 40% ammonium sulfate insoluble globulin fractions did not satisfactorily sensitize erythrocytes to agglutinate in the presence of either group specific polysaccharide of group A beta-hemolytic strepticocci or antigen produced during colony formation. Antibody purified by affinity chromatography sensitized the erythrocytes to rapidly agglutinate in the presence of either antigen. No spontaneous or "pseudo-immune" agglutination occured when the sensitized erythrocytes were suspended in human serum. Such sensitized human cells, while more difficult to prepare than sensitized staphylococci, should be suitable for detecting bacterial or viral antigens in vivo.