Scope and Method of Study: This study is focused on developing methodologies for rapid and sensitive detection of Staphylococcus aureus enterotoxins and enterotoxin genes. S. aureus produces twenty serological types of enterotoxins. Enterotoxins are heat resistant proteins that may cause food poisoning outbreaks. Besides being the causative agents of foodborne intoxications, enterotoxins are also superantigens and select agents. Many methodologies have been developed in the past for detection of enterotoxins from foods. Sensitivity in detection methods is very important as these toxins are potent in minute quantities. The existing methods have many constraints, as it is not easy to detect toxins from complex environments such as foods due to interference from organic matter. We have developed a very sensitive and rapid immunomagnetic PCR signal amplification (iPCR-SA) assay for detection of enterotoxins in foods. The assay involves, capture of toxin antigens in foods by primary antibody coated paramagnetic beads. A conjugate consisting of secondary antibody covalently linked to reporter DNA was amplified using real-time PCR. Our next objective was to develop a rapid method for detection of enterotoxin genes from S. aureus, which may be present in foods as the result of post-process contamination. Seventeen sets of primers were designed for this purpose. All known coding sequences of enterotoxin genes were aligned using ClustalW program provided by Vector NTI 10, software. Primers were selected in consensus regions of each toxin group, and the resulting amplicon was in a region of heterogeneity. A ~500 bp region thus amplified was sequenced and analyzed by the BLAST algorithm. Isolates of S. aureus from foods, humans, and cows were analyzed using the primer array

Findings and Conclusions: The limit of detection of iPCR-SA assay was less than 7.5 fg/ml or g of various foods that were analyzed. The assay was not inhibited by the presence of other organic matters that are present in foods, and could be completed within 5-6 h. Enterotoxin genes were amplified using primer array in seventeen individual PCR reactions. Amplification followed by sequencing and analysis enabled quick identification of enterotoxin genes. Some strains harboured as many as 7 different toxin genes and differences in sequences of toxin genes from our isolates were identified.