Quantitative Detection of Staphylococcal Enterotoxin B in Food by Gel-Diffusion Methods

Abstract

RECOVERY of coagulase-positive Staphylo¬ coccus aureus from food implicated in a foodpoisoning outbreak is only circumstantial evi¬ dence that the correct etiological agent has been found. Even the determination by animal studies that the strain isolated is capable of pro¬ ducing enterotoxin does not prove that it did so in the food. Positive proof depends on dem¬ onstration of the enterotoxin in the food itself.

A Rapid Sensitive Assay for Staphylococcal Enterotoxin and a Comparison of Serological Methods

“…HA-inhibition, passive HA, and the quantitative precipitin test have not been used with food samples. It seemed that these procedures would be less influenced by the presence of the nonspecific substances that affect immunodiffusion; thus, the lengthy procedures described for processing food extracts could be eliminated (4,14). In addition, HA should permit the detection of smaller amounts of enterotoxin than do the other methods without the necessity of concentrating the food extracts.…”

“…The data in Table 2 were obtained with frozen foods that had been thawed but not cooked before homogenization and the addition of enterotoxin; Table 3 shows results obtained with cooked products. It was difficult to clarify the liquid separated from the homogenates of the uncooked tuna or custard pies so that it was not possible (4,13,14). The mean end point for about 30 HA tests with purified enterotoxin was 0.0015 ,ug per ml (or 0.0007 ug, the actual amount in the 0.5-ml volume of the test).…”

“…Methods for immunodiffusion in agar, quantitative precipitin assays, hemagglutination (HA)-inhibition, and immunofluorescence have been described for this purpose (8,9,11,15,17,21,23). Measure (4,12,13,14,19,20). HA-inhibition, passive HA, and the quantitative precipitin test have not been used with food samples.…”

“…Sinitsyn (22) 6.4) and were heated at 50 C for 15 min. After standing for 45 min at room temperature, they were centrifuged at about 15,000 X g for 20 min in a Servall SS-1 centrifuge at 4 C. The clear liquid portion between the sediment and the top fat layer was removed with a syringe having an 18-gauge needle and then was filtered through a single layer of paper towel (Scott Wipers 590, Scott Paper Co., Chester, Pa.) (14). Cheese and milk were prepared essentially as described by Read et al (19,20).…”

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(8,9,11,15,17,21,23 (4,12,13,14,19,20Formalin-preserved sheep erythrocytes (SRBC) were obtained from Difco. They were washed once with 0.038 M NaHSO, in 0.85% saline and then twice with saline.

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