Detection and quantification of staphylococcal enterotoxin A in foods with specific and sensitive polyclonal antibodies

Staphyloccocus aureus is reported to be one of the most frequent pathogens involved in food-borne diseases associated with dairy products, especially with raw milk cheese. Some strains produce enterotoxins as Staphylococcal enterotoxin A (SEA) which is involved in 75% of food poisoning outbreaks. Actually few methods are both sensitive and specific enough for confirming the diagnosis of staphylococcal food poisoning. In this work, an Enzyme-Linked ImmunoSorbent Assay (ELISA) was set up and optimised to detect SEA in milk and cheese. Various anti-SEA antibodies: polyclonal sera, anti-peptide polyclonal sera and monoclonal antibodies, used for the capture and or detection steps were compared and analysed. The mouse anti-whole SEA polyclonal serum, used as detection detected 32 pg/ml SEA in buffer and 64 pg/ml in milk. These concentrations were well under the limit set for food safety. This assay was also highly specific of SEA and no cross-reaction was observed with the other staphylococcal enterotoxins. In contaminated cheese samples the time of enterotoxin extraction was reduced by using ultrafiltration method instead of dialysis and the detection limits were 1.5–2.5 and 1.9–3 times more sensitive than a commercial kit and the official method, respectively. Preliminary study of SEA detection with the piezoelectric immunosensor allowed detecting and quantifying SEA within 10 min in unprocessed food but the sensitivity was not sufficient. The ELISA assay with mouse antibodies is likely suitable for SEA routine detection not only in dairy product but also in various foods as sauce and liver mousse.