Detection of Staphylococcal Enterotoxins in Foods

Abstract

Procedures were developed for assay of staphylococcal enterotoxins in foods, using microslide gel double diffusion test.(1) Foods were prepared for assay by addition of water (homogenization or mashing in case of cereal foods) adjustment of pH to 7.4-7.6, blending, and centrifugation. The supernatant fluids were then adjusted to pH 4.5 (in case of animal foods) or pH 6.0, and centrifuged. Supernatant fluids taken at pH 4.5 were readjusted to pH 6.0, and centrifuged. From these supernatant fluids, enterotoxins were partially purified by adsorption on CM-Sephadex C-50 equilibrated with 0.01M sodium phosphate (pH 6.0), washing with 0.01M sodium phosphate (pH 6.0), then eluted with 0.2M sodium chloride in 0.1M sodium phosphate (pH 7.6), and concentrated by dialysis against polyethylene glycol.Adequate dosage levels of CM-Sephadex in the batch ion exchange for various foods were determined, individually.(2) By these procedures, enterotoxins were detected in 12 out of 16 foods suspected for cause of poisoning outbreaks. Enterotoxin A (50%) and A+D (33%) were predominant types. Concentrations of enterotoxins detected in foods were ranging up to 0.3μg/g, and estimated at 0.05μg/g on the average. In 4 outbreaks, neither enterotoxins nor enterotoxin-producing staphylococci were isolated from the suspected foods.(3) The extract from suspected cream puff containg 4.5μg of enterotoxin A induced emetic responses in a volunteer by feeding test.