Measurement of staphylococcal protein A and detection of protein A-carrying staphylococcus strains by a competitive ELISA method.

A competitive ELISA for the estimation of staphylococcal protein A is described. Tetanus toxoid is insolubilized on polystyrene and incubated with human antitoxin, which renders the Fc-piece of this antibody freely accessible to protein A. The binding of the latter is demonstrated by its competition with protein A-phosphatase conjugate. The method has been shown to be sensitive and reproducible. It has been used for the detection of protein A in culture supernatants and on living pathogenic staphylococci. The test could therefore be of diagnostic value. Protein A is also present in extracts of food contaminated with enterotoxic staphylococci. It can be eliminated by a simple absorption with insoluble porcine IgG.