Investigations were performed to avoid cross-reactions in the enzyme linked immunosorbent assay, using the sandwich technique, for detection of Staphylococcus aureus enterotoxin type B. Non-specific reactions can be caused by cross-reacting antigens and by Protein A, produced by S. aureus. The former reactions can be prevented by adsorption with culture filtrate of non-toxin type B producing strains. The latter reaction is caused by the binding of Protein A to the Fc fragments of the IgG antibodies. Interference by Protein A was completely eliminated by using the F(ab')2 fragments of the IgG antibodies.

ELISA experiments in which these purified F(ab')2 fragments were used resulted in a highly specific detection of entertoxin type B, both in culture filtrates and in foods.