Identification of Nonclassical Enterotoxin Genes in Stored Staphylococcus aureus Isolates From Milk of Subclinical Mastitis Cows in Sumedang Regency.

Staphylococcal enterotoxins (SEs) are thermostable superantigenic proteins produced by Staphylococcus aureus (S. aureus) that are responsible for staphylococcal food poisoning (SFP) in humans. SEs are classified into classical and nonclassical types, with increasing attention given to the nonclassical due to their potential role in food safety. Therefore, this study is aimed at identifying the presence and distribution of selected nonclassical SE genes (sek, sel, sem, sen, seo, sep, seq, and ser) in 22 stored biological isolates of S. aureus obtained from milk of dairy cows with subclinical mastitis at Mekar Bakti Farm, Pamulihan District, Sumedang Regency, Indonesia. The presence of nonclassical SE genes was investigated using multiplex polymerase chain reaction (PCR). The results showed that the sek gene was detected in 90.9% (20/22) of the isolates, whereas the sep gene was identified in 4.5% (1/22), with an isolate harboring both genes. In addition, no amplification was observed for the remaining target genes. Proportions were presented with 95% confidence intervals to reflect uncertainty associated with the limited sample size. As this study was based on PCR detection, the results demonstrated the presence of enterotoxin-associated genes but did not necessarily reflect gene expression, virulence activity, or underlying regulatory mechanisms. The detection of enterotoxin-associated genes in isolates from subclinical mastitis milk indicated their potential relevance at the animal-food interface. These findings provide baseline data for molecular surveillance and support further studies incorporating genomic or expression-based approaches to better characterize enterotoxigenic S. aureus in dairy systems.