A New Immunoassay for the Detection of Staphylococcal Enterotoxins G (SEG), H (SEH) and I (SEI)

Introduction: Staphylococcal food poisoning is one of the most common foodborne diseases resulting from the ingestion of staphylococcal enterotoxins (SEs) preformed in foods by enterotoxigenic strains of coagulase-positive staphylococci, mainly Staphylococcus aureus. Immunological methods are considered as the most practical and powerful methods for the analysis of SEs in foods because they give sensitive and reliable results. To date, the commercially available test kits are able to detect SEA to SEE, but not SEG, SEH and SEI.

Purpose: The goal of this study was to develop and briefly evaluate an immunoassay for the screening of SEG, SEH and SEI in food products.

Methods: Using recombinant SEG, SEH and SEI as immunogens, polyclonal antibodies were raised in rabbit and then immunopurified and conjugated to alkaline phosphatase. The purified antibodies and the conjugates were used to develop a two-step sandwich ELISA assay adapted to the VIDAS automated system.

Results: When tested individually, the antibodies showed no significant cross-reactivity with the other non-related toxins (for example, SEA, SEB, SEC, SED, SEE, SEH, SEI did not cross-react with anti-SEG antibodies) tested at a concentration of 100 ng/ml. In a multiplex assay, the limit of detection (LOD) using pure toxins was < 0.1 ng/ml. The ELISA detected SEG, SEH and SEI in two artificially contaminated food products (raw milk cheese and meat product) in a dose-dependent manner, with an LOD <0.4 ng of toxin per g of products when the food extracts were pre-concentrated with polyethylene glycol 20,000.

Significance: The new ELISA in this study showed high sensitivity and specificity for the detection of SEG, SEH and SEI in food samples, providing a promising tool to ensure food safety.