Staphylococcus aureus Bacteria Resistant to Methicillin in Raw Milk

The presence of antibiotic-resistant strains of Staphylococcus aureus (particularly methicillin-resistant strains) in food of animal origin is considered as a severe threat to human health due to numerous clinical complications. This study tended to determine the prevalence of methicillin-resistant S. aureus in samples of raw milk distributed in Tehran using antibiotic susceptibility testing methods. In the present study, 100 raw milk samples were taken from the centres of production and purchase of milk and its products in Tehran; the samples were evaluated by culture in terms of infection with coagulase-positive S. aureus. Finally, antibiotic resistance pattern of isolates was studied using disk diffusion agar. The average colony count was estimated. Raw milk cultures were estimated at 2×105-4×105 cfu/ml. Based on the results of culture, 36 samples of raw milk tested were icnfected with positive-coagulase S. aureus. The highest susceptibility was observed for ciprofloxacin and gentamicin (100%) and the highest resistance was observed to penicillin, tobramycin, oxacillin and ceftazidime. The results showed the prevalence of infection of raw milk with S. aureus. Moreover, prevalence of S. aureus resistant to a wide range of antibiotics, more importantly, methicillin resistant, was significant in the tested samples. Therefore, adherence to and control of sanitation in different stages of production, supply and consumption of milk can prevent human infection.