Detection of Methicillin-resistant Staphylococcus aureus (MRSA) resistant to vancomycin and linezolid in bulk tank milk by E-test method

Staphylococcus aureus is considered a serious threat to public health, besides is one of the most common causes of subclinical mastitis in dairy cows. Therefore, especially methicillin-resistant Staphylococcus aureus (MRSA) is among the most critical reasons for antibiotic treatment. Monitoring the antibiotic resistance of MRSA from livestock animals and foods is of great significance. The E-test method is a suitable option for detecting antibiotics' minimum inhibition concentration (MIC) value because it is an easy and fast assay to perform. This study aimed to detect vancomycin, teicoplanin, and linezolid resistance of milk-borne 34 MRSA isolates with subclinical mastitis by the E-test method to determine MIC values. The study determined that 8.8% of MRSA isolates isolated from milk with subclinical mastitis were also resistant to vancomycin and 11.7% to linezolid, while none of the isolates were determined to be resistant to teicoplanin, according to EUCAST. The data obtained from the study reveal that the efficacy of vancomycin and linezolid antibiotics, which are commonly used against MRSA infections, are in danger. Especially before MRSA treatment, MIC values of antibiotics should be determined, and appropriate antibiotics should be used in effective doses.