Distribution, polymorphism and temporal expression of egc in Staphylococcus aureus isolates from various foods in China

Staphylococcal food poisoning (SFP) is characterized by diarrhea and vomiting resulting from the ingestion of staphylococcal enterotoxins (SEs) contaminated foods. The genome-located enterotoxin gene cluster (egc) encodes superantigens performed different clinical severities than traditional SEs. In this study, we identified 336 Staphylococcus aureus isolates from various foods in China and investigated the presences of egc, 5 classical SE genes, accessory gene regulator (agr) and sarA. Subsequently, the egc subtypes were assayed and the mRNA expression of egc and relative genes in the cell cycle were analyzed in selected isolates. As a result, egc was more prevalent than all traditional SE genes in foodborne S. aureus isolates, and egc1 was the predominant subtype. During the growth cycle, the expression patterns of egc and those of traditional SE genes were similar in tested isolates: the enterotoxin mRNAs peaked at the post-exponential growth phase and then rapidly decreased. Simultaneously, the agr system was activated and the sarA expression was enhanced. However, ZJY58, the only selected isolate which did not harbor agr, performed significantly lower peak of egc expression than other isolates. Hence, these data of gene typing and expression described a general profile of egc in food-derived S. aureus, and would have potential use in the control of SFP.

► The egc is the most prevalent enterotoxin genes in foodborne S. aureus. ► The predominant subtype of egc in foodborne S. aureus is egc1. ► The temporal expression patterns of egc are similar as classical enterotoxin genes. ► The egc expression may have potential relation with agr system.