Prevalence of Methicillin-Resistant Staphylococcus Aureus and Antibiotic Residue in Pasteurized and Raw Farm Milk in Tehran

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.

This was a cross-sectional study conducted from April to July 2020. 250 samples (200 samples of raw milk in farms around Tehran and 50 samples of pasteurized milk) were cultured to evaluate the occurrence of S. aureus and its antimicrobial susceptibility profile to 7 antimicrobial panels. Hansen Kit was used to monitor antibiotic residue in milk.

63 S. aureus isolates (25.2%) were detected from 250 milk samples. Among 200 raw milk samples, 48 (24%) S. aureus isolates were detected and no strain of S. aureus was isolated from pasteurized milk. The highest rates of resistance belonged to ampicillin (95.8%), amoxicillin/clavulanic acid (87.5%), tetracycline (50%), and cefoxitin (45.8%). Moreover, 43 (17.2%) out of 250 milk samples had antibiotic residue in the antibiotic residue test using Danish Hansen kit.

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