SENSITIZED SHEEP RED CELLS AS A REACTANT FOR STAPHYLOCOCCUS AUREUS PROTEIN A

Abstract

Staphylococci with cell‐bound protein A reacted with sensitized sheep red cells in a simple slide reaction with agglutination. Extracellular protein A proved capable of preventing the sensitized sheep red cells from reacting with cultures of Staph, aureus strains containing protein A. This confirms the reactivity of protein A with free Fc‐fragments of IgG on the surface of the sensitized sheep red cells as the cause of haemagglutination. The choice of culture medium proved important for demonstrating protein A. Peptone‐free media proved clearly unsuitable. 341 routinely isolated strains of Staph. aureus were examined for agglutination of sensitized sheep red cells in the slide test and for tube‐agglutination of sensitized sheep red cells with broth culture filtrate. 88.3 per cent of the strains were positive if examined on slides, while 6.7 per cent of the strains contained no cell‐bound or free protein A demonstrable by either method. Among the methicillin resistant strains, 50 per cent showed no agglutination on slide. Antibiotic‐sensitive strains belonging to phage group II tended to have weaker protein A reactivity than other groups.