Visual Screening with Enzyme Immunoassay for Staphylococcal Enterotoxins in Foods: Collaborative Study

Abstract

Abstract Selected foods containing 4–10 ng each of a mixture of Staphylococcus aureus enterotoxin serotypes A–E were tested by 15 collaborators. An enzyme-linked immunosorbent assay (EIA) was used with polyvalent antisera to these serotypes in a polyclonal antibody double “sandwich” configuration. Controls were free of toxin. Foods (25 g test samples) were homogenized with Tris (0.25M, pH 8.0) and centrifuged. The food extract was filtered through cotton and mixed with sample additive. For the EIA, 200 μL aliquots of the treated extracts were added to previously washed microtiter wells coated with antibody to staphylococcal enterotoxin serotypes A–E. Wells were washed and treated with the polyvalent antisera (A–E)-enzyme conjugate, and then washed again. Substrate was added, and wells were incubated. After incubation, stop solution was added. Results were determined visually and by measuring absorbance using a microtiter plate reader. In foods containing enterotoxin, bluish-green color was developed (positive result). Test solutions with absorbances >0.200 were considered positive; those with absorbances ≤0.200 were negative. The method is sensitive and specific, and allows the rapid assay of staphylococcal enterotoxins in foods without differentiating their serotypes. The method has been adopted first action by AOAC INTERNATIONAL.