PREVALENCE OF METHICILLIN-RESISTANT STAPHYLOCOCCUS AUREUS IN RAW COW'S MILK COLLECTED FROM STORAGE TANKS AND MILK SUPPLY CENTERS IN URMIA CITY, IRAN, AND DETERMINATION OF THEIR ANTIBIOTIC RESISTANCE

Staphylococcus aureus (S. aureus) is one of the most important food-borne pathogens that causes staphylococcal poisoning in humans. This study aimed to isolate and identify Staphylococcus aureus and methicillin-resistant Staphylococcus aureus (MRSA) in raw cow milk, phenotypic and genotypic identification of them, and determination of the resistance pattern of isolates in Urmia city, Iran.

290 samples of raw cow's milk from May to December 2016 were collected from milk storage tanks in cattle farms and milk supply places in Urmia city, Iran, and were transferred to the food hygiene laboratory under sterile and cold conditions for their isolation process. Staphylococcus aureus was transferred using the usual microbiological and biochemical methods. To confirm coagulase positive isolates, nuc gene identification method was used. In order to identify the phenotypic isolates resistant to methicillin, Kirby-Bauer disk diffusion method and genotypic identification of mecA gene were used.

44 isolates were collected from 290 milk samples (144 samples from milk storage tanks and 146 samples from milk supply places), which from them, 14 isolates (7.9%) were from milk storage tanks and 30 isolates (20.5%) were from the milk supply places. The presence of Staphylococcus aureus in the samples was confirmed by polymerase chain reaction. Out of a total of 44 isolates, 7 isolates (16%) were resistant to Oxacillin, which from them, one isolate (7.1%) was from the tanks and 6 isolates (20%) were from the raw milk supply centers. They were detected as Staphylococcus aureus isolates which were resistant to Methicillin. The highest level of resistance of the isolates belonged to Penicillin (59.1%). None of the isolates showed resistance to Vancomycin, Tobramycin, and Gentamicin. From five isolates (4.1%) which had mecA gene, 4 isolates (13.3%) were related to milk supply centers and one isolate (7.1%) were related to milk tanks.

According to the obtained results, the prevalence of Staphylococcus aureus and MRSA in milk supply centers is higher than that in the milk storage tanks. These results indicate secondary contamination and non-observance of hygienic principles during transportation and supply of milk.