In Vitro Assay of Staphylococcal Enterotoxins A and B from Milk

Abstract

Procedures were developed for assay of staphylococcal enterotoxins A and B in milk, using single- and double-agar gel diffusion. Milk was prepared for assay by acidification, filtration, neutralization, heating, centrifugation, and the supernatant fluid was used as an antigen for gel diffusion or it was concentrated 20 times in a dialysis sac immersed in polyvinylpyrrolidone. The concentrated fluid was then acidified, centrifuged, neutralized, heated, extracted with chloroform, recentrifuged, and the supernatant fluid added to double-diffusion enterotoxin assay tubes. These procedures were applied to raw, pasteurized skim, pasteurized homogenized, frozen pasteurized homogenized, condensed, and dry milks. The single-diffusion enterotoxin assay system was sensitive to enterotoxin A and B concentrations as low as 0.33 and 1.0 /μg per milliliter of milk, respectively. With double diffusion, minimum detectable levels of enterotoxins A and B were 0.25 and 0.63μg per milliliter of milk, respectively. When concentration procedures were used, the double-diffusion test was sensitive to respective enterotoxin A and B levels of 0.015 and 0.03μg per milliliter of milk.