Abstract

Reports of methicillin-resistant Staphylococcus aureus (MRSA) in food have become more frequent in recent years. The aim of this study was to estimate the presence of MRSA in raw milk, pasteurized milk and ice cream in Tabriz by culture and polymerase chain reaction (PCR) techniques, as well as the determination of their antimicrobial susceptibility. For this purpose, 300 samples of raw milk, pasteurized milk and ice cream were collected from different sellers in Tabriz. They were first evaluated for contamination by coagulase positive S. aureus through culturing method, and then the isolates were subjected to PCR method according to nuc gene in order to confirm S. aureus andmethicillin resistance gene (mecA). Finally the antimicrobial resistance trend of the isolates was investigated by disc diffusion agar method. The cultured samples indicated that 50 (50%) of raw milk samples, 2 (2%) of pasteurized milk samples and 26 (26%) of ice cream samples were contaminated by S.aureus. Forty five, 1 and 23 of these isolates, respectively were confirmed to be S.aureus based on PCR using nuc gene primer. From the total of 69 isolates containing nuc gene, 20 isolates had the resistant mecA gene. Of the 69 isolates, 17 isolates showed simultaneous resistance against 4 antibiotics, 18 against 5 antibiotics, 8 against 6 antibiotics, 8 against 7 antibiotics, 7 against 8 antibiotics, 6 against 9 antibiotics, 2 against 10 antibiotics and 3 isolates against 11 antibiotics. In other words 100% of the isolates showed simultaneous resistance to more than 3 antibiotics. The results provide evidence that the presence of antimicrobial resistant strains of S. aureus has become remarkably widespread in food samples. This calls for better control of the sources of food contamination and as well as the spread of antimicrobial-resistance organisms.

Key words: Methicillin-resistant Staphylococcus aureus, milk, ice cream, polymerase chain reaction (PCR).