Detection of Enterotoxin A Gene (sea) and Determination of Different Biotypes of Staphylococcus Aureus Isolates From Milk and Cheese in Khuzestan Province, Iran

There has been a growing concern about the potential transmission of Staphylococcus aureus strains among human and animal species through the consumption and handling of foods of animal origin.

The present study aimed to determine the source and possible route of milk and dairy contamination in Khuzestan province of Iran.

A total of 150 raw cow’s milk and 50 traditional cheese samples were collected from local markets in different cities of Khuzestan province, Iran. Presumptive colonies on Baird Parker Agar were subjected to the Polymerase Chain Reaction assay in order to identify the Staphylococcus genus, thermonuclease gene specific for S. aureus, enterotoxigenic gene (sea), and coa gene for coagulase gene. Moreover, biotyping of S. aureus strains was implemented based on Devriese’s system, and the antibiotic susceptibility testing (five antibiotics) was carried out.

Overall, 80 Staphylococcus spp. was isolated from the samples. The PCR was performed and, as the result, 23 S. aureus were confirmed, out of which 2 isolates (8.6%) belonged to the human ecovar and 17 isolates (73.9%) belonged to the non-host specific (NHS) biotype, whereas 4 isolates (17.3%) remained unclassified. Furthermore, sea gene and coagulase genes were detected in 3 and 22 isolates, respectively. The rates for contamination with S. aureus in milk and in cheese were 15% (19 samples) and 8% (4 samples), respectively. Overall, 4%, 9%, 17%, 35%, and 56% of isolates were found resistant to gentamicin, erythromycin, oxacillin, trimethoprim, and penicillin, respectively.

The local milk and cheese supplied in the given area were contaminated with antibiotic-resistant and enterotoxigenic staphylococci. Therefore, it was recommended that the supply chain of these materials should be carefully monitored in order to prevent the complications caused by the contamination with these ecovars.