Improved reversed passive hemagglutination for simple and rapid detection of staphycococcal enterotoxins A approximately E in food

Detection and identification of staphylococcal enterotoxins in food or culture filtrates were performed using the reversed passive hemagglutination (RPHA) technique, with formalized sheep red blood cells (FSRBC) sensitized with immunologlobulins of anti-A, B, C, D, and E rabbit hyperimmune sera fractionated by affinity chromatography. The FSRBC sensitized with anti-A approximately E immunoglobulins showed a high level of reactivity and specificity in RPHA, against homologous types of purified enterotoxins and culture filtrates of toxin-producing strains. No non-specific reactions with various ingredients in foods nor cross-reactions among enterotoxin types were observed. The minimum amount of enterotoxins in foods detected by RPHA was calculated to be 0.01 micorgram/g without concentration, and the recovery rate of experimentally added toxins was calculated to be about 80%. Under routine laboratory practice, detection and identification of enterotoxins from incriminated foods of five food poisoning outbreaks were performed by RPHA within 3 hr after reception of the specimens. Among them, three were determined to be enterotoxin A food poisoning, one to be toxin C and the rest to be intoxication of A and D. The concentrations of the toxins was between 0.014 and 3.65 microgram per gram of food.

Heterogeneity of staphylococcal enterotoxin A on isoelectric focusing and disc electrophoresis

Heterogeneity of purified staphylococcal enterotoxin A, obtained from a culture supernatant of Staphylococcus aureus, strain 13N-2909, was demonstrated by isoelectric focusing. The toxin was composed of three immunologically identical fractions with isoelectric points of 6.5, 7.0 and approximately 8.0. Heterogeneity of the toxin was also shown by disc electrophoresis. At pH 8.0 and 9.4 two major bands and a faint minor band were observed, while at pH 4.3 only one band was observed. The faster-moving band for the anode in disc electrophoresis at pH 9.4 was found to correspond with the pI 6.5 component from isoelectric focusing, while the slower-moving band corresponded with the pI 7.0 component. From the results of the electrophoretic migration tests of the toxin, the components corresponding to the two major bands found in disc electrophoresis at pH 9.4 were considered to be charge isomers.