Mohammad Mehdi Soltan Dallal - Department of Pathobiology, School of Health, Tehran University of Medical Sciences, Tehran, Iran
Zohreh Didar - Department of Food Science and Technology, Neyshabur Branch, Islamic Azad University, Neyshabur, Iran
Mohammad Reza Mohammadi - Department of Bacteriology, Faculty of Medical Sciences, Tarbiat Modares University, Tehran, Iran
Saeed Vahedi - Department of Anesthesiology, School of Paramedical Sciences, Tehran University of Medical Sciences, Tehran, Iran
Ronak Bakhtiari - Department of Pathobiology, School of Health, Tehran University of Medical Sciences, Tehran, Iran
Seyedeh Zohre Mirbagheri - Department of Pathobiology, School of Health, Tehran University of Medical Sciences, Tehran, Iran
Hedroosha Molla Agha Mirzaei - Food Microbiology Research Center, Tehran University of Medical Sciences, Tehran, Iran

Background: There is a global threat of methicillin-resistant Staphylococcus aureus (S. aureus or MRSA), which has been regarded as a priority pathogen by the world health organization (WHO). Livestock and its products are the sources of MRSA which can often occur in poor breeding conditions. The present study aims to investigate the prevalence of MRSA and the rate of antibiotic residue in pasteurized and raw farm milk. Methods: This was a cross-sectional study conducted from April to July ۲۰۲۰. ۲۵۰ samples (۲۰۰ samples of raw milk in farms around Tehran and ۵۰ samples of pasteurized milk) were cultured to evaluate the occurrence of S. aureus and its antimicrobial susceptibility profile to ۷ antimicrobial panels. Hansen Kit was used to monitor antibiotic residue in milk. Results: ۶۳ S. aureus isolates (۲۵.۲%) were detected from ۲۵۰ milk samples. Among ۲۰۰ raw milk samples, ۴۸ (۲۴%) S. aureus isolates were detected and no strain of S. aureus was isolated from pasteurized milk. The highest rates of resistance belonged to ampicillin (۹۵.۸%), amoxicillin/clavulanic acid (۸۷.۵%), tetracycline (۵۰%), and cefoxitin (۴۵.۸%). Moreover, ۴۳ (۱۷.۲%) out of ۲۵۰ milk samples had antibiotic residue in the antibiotic residue test using Danish Hansen kit. Conclusion: The present study indicates a high prevalence of subclinical S. aureus in dairy herds in Tehran, Iran. The milk contaminated with S. aureus and MRSA, posed a risk to public health owing to the presence of a phenotype resistant to very common antibiotics

Milk, Staphylococcus aureus, Methicillin, Anti-bacterial agents