The Frequency of Staphylococcus aureus Classical Enterotoxin Genes in Raw Milk Samples in Zanjan, Iran

Background: Staphylococcus aureus is one of the major causes of food poisoning. Since milk is a nutritious source of proteins and vitamins, it could provide the optimal conditions for the growth of several bacterial pathogens, such as S. aureus. The present study aimed to assess the frequency of Staphylococcus aureus classical enterotoxin genes in raw milk samples in Zanjan, Iran. Methods: In total, 82 bovine, unpasteurized milk samples were collected from the dairy farms in various rural areas in Zanjan, Iran. The isolation and identification of S. aureus were performed using the Baird-Parker agar, routine biochemical tests, and polymerase chain reaction (PCR) targeting the S. aureus-specific femA gene. In addition, staphylococcal enterotoxin genes (e.g., sea, seb, sec, sed, and see) were assessed using PCR. Results: Following the appearance of yellow colonies with yellow zones on Mannitol salt agar, 21 S. aureus isolates (25.6%) were detected. In total, 80.9% of the isolates were positive for the presence of SE genes, and the most frequent SE gene was sea (88.2%), followed by see (58.8%), and seb (52.9%). Furthermore, 76.5% of the isolates had two or more SE genes simultaneously. Conclusion: According to the results, the presence of enterotoxigenic S. aureus in the studied raw milk samples confirmed the possible risk posed on the public health. Therefore, it is recommended that the quality of dairy product quality programs be optimized in order to intensify the sanitary inspection of these products.