DETECTION OF STAPHYLOCOCCUS AUREUS PRODUCTS IN FOODS USING ENZYME LINKED IMMUNOSORBENT ASSAY AND SPECTROPHOTOMETRIC THERMONUCLEASE ASSAY

Abstract

The comparative sensitivity of an enzyme linked immunosorbent assay (ELISA) using four different antistaphylococcal antisera and a spectrophotometric assay for thermonuclease were determined using cheese and ravioli samples seeded with strains of Staphylococcus aureus and S. epidermidis. The ELISA used antisera to enterotoxin A, enterotoxin B, S. aureus strains 14609 (human), and UNH‐570 (bovine). The 570 ELISA and spectrophotometric thermonuclease assay were of comparable sensitivity and detected seeded culture in concentrations as low as 2 × 107 CFU/g of cheese. A simple two hour method for extracting thermonuclease from foods was 50% efficient when as little as 50 ng of purified enzyme was seeded per g of cheese. Analyses of 43 commercial cheeses for viable S. aureus found five (12%) positive with 3 × 104 CFU/g of cheese being the highest counts detected. All samples were negative by ELISA and thermonuclease assay. A simple screening procedure for demonstration of S. aureus contamination of foods is discussed.