egc characterization of enterotoxigenic Staphylococcus aureus isolates obtained from raw milk and cheese

Abstract

Genes encoding staphylococcal enterotoxins (SEs) are carried by mobile genetic elements, and enterotoxin gene clusters (egc) are pathogenicity island-borne structures comprising several SE genes, which are frequently found among clinical Staphylococcus aureus isolates. In the present study, we investigated the distribution and the genetic variability of egc loci in S. aureus strains isolated from raw milk and soft cheese in Minas Gerais, Brazil. Ninety-two isolates were submitted to PCR detection of individual egc-borne SE genes (seg, sei, sem, sen, seo, seu), and egc loci were typed using PCR-RFLP. PCR products of egc positive isolates were sequenced. Ninety-one isolates harbored at least one SE gene, which generated 14 different genotypes. The sei gene was the most widely distributed (97.8%), and was found in combination with seg in 49 isolates (53.3%). Altogether, a complete set of individual egc genes was detected in 37 isolates (40%). However, egc loci were detected by PCR-RFLP in only 4 isolates, and classified as egc1 (n = 2), egc3 (n = 1), and egc4 (n = 1). This investigation demonstrated the low occurrence of the egc in S. aureus isolated from dairy products. However, the frequency of complete sets of individual egc-borne genes reflects either the presence of these SE genes outside egc or the existence of new egc types in these strains.