Detection of mecA gene and methicillin-resistant Staphylococcus aureus (MRSA) isolated from milk and risk factors from farms in Probolinggo, Indonesia

Background:Staphylococcus aureus is commonly found in dairy cows and is a source of contamination in milk. S. aureus that are resistant to beta-lactam antibiotics are referred to as methicillin-resistant Staphylococcus aureus (MRSA). The spread of MRSA cannot be separated from sanitation management during milking; it can originate from milk collected from the udder or from the hands of farmers during the milking process. The purpose of this study was to examine the level of MRSA contamination in dairy cow's milk and farmer's hand swabs. Methods: A total of 109 samples of dairy cow's milk and 41 samples of farmers' hand swabs were collected at a dairy farm in Probolinggo, East Java, Indonesia. Samples were cultured and purified using mannitol salt agar (MSA). The profile of S. aureus resistance was established by disk diffusion test using a disk of beta-lactam antibiotics, namely oxacillin and cefoxitin. Results: The S. aureus isolates that were resistant to oxacillin and cefoxitin antibiotics were then tested for oxacillin resistance screening agar base (ORSAB) as a confirmation test for MRSA identity. S. aureus isolates suspected to be MRSA were then tested genotypically by polymerase chain reaction (PCR) method to detect the presence of the mecA gene. The results of the isolation and identification found 80 isolates (53.33%) of S. aureus. The results of the resistance test found that 42 isolates (15%) of S. aureus were resistant to oxacillin and 10 isolates (12.5%) were resistant to cefoxitin. The ORSAB test found as many as 20 isolates (47.62%) were positive for MRSA. In PCR testing to detect the presence of the mecA gene, three isolates (30%) were positive for the mecA gene. Conclusions: This study shows that several S. aureus isolates were MRSA and had the gene encoding mecA in dairy farms.