Molecular Characterization and Antibiotic Resistance Profile of Methicillin-Resistant Staphylococcus aureus (MRSA) Strains Isolated From Milk Samples of Apparently Healthy Cattle in Hamedan, Iran

Staphylococcus aureus, as a major food-borne pathogen, is the most commonly isolated bacterium from bovine mastitis. However, some S. aureus strains exhibit a high rate of antibiotic resistance, among which, methicillin-resistant S. aureus (MRSA) is very important. The present study was conducted to isolate, characterize, and determine the antibiotic resistance profile of MRSA strains in milk.

Staphylococcus aureus strains were isolated and identified from 415 milk samples collected from apparently healthy cattle in Hamedan province, Iran. Molecular characteristics of the strains were identified using multiplex polymerase chain reaction (PCR) and the antibiotic resistance profile of the isolates was determined by Kirby-Bauer disk diffusion susceptibility test.

A total of 76 S. aureus strains were isolated and identified. The PCR results indicated that 50 (65.78%) isolates possessed mecA gene and were found to be MRSA strains. Twelve isolates (15.78%) showed phenotypic resistance to oxacillin in disk diffusion method. All 76 S. aureus isolates (100%) were resistant to penicillin and susceptible to ciprofloxacin and gentamicin.

The results of the present study indicated that bovine milk may contain MRSA strains and this is worrying as these isolates may transfer multi-drug resistance to the isolates that circulate among humans, animals, and food chains.