Frequency and Antimicrobial Susceptibility of Methicillin and Vancomycin-Resistant Staphylococcus aureus from Bovine Milk

Abstract

The increase in resistance pattern of Staphylococcus aureus (S. aureus) has been an emerging threat in therapeutic areas of the dairy industry throughout the globe. The current study was conducted in bovines of district Faisalabad, Pakistan to investigate the phenotypic prevalence of methicillin-resistant (MRSA) and vancomycin-resistant S. aureus (VRSA) in milk samples positive for subclinical mastitis. The study further aimed to assess the associated risk factors and antimicrobial susceptibility pattern against MRSA and VRSA isolates. A total of 385 milk samples (n=193 cattle; n=192 buffalo) collected and screened for subclinical mastitis by surf field mastitis test (SFMT) were further subjected to standard microbiological techniques for the isolation of S. aureus. The positive isolates of S. aureus were phenotypically evaluated for MRSA and VRSA by the disc diffusion method. The study results revealed that out of 385 milk samples, 45.97% (177/385) samples were found positive for subclinical mastitis on SFMT while 37.14% (143/385) samples were confirmed for the presence of S. aureus. Out of these S. aureus isolates, MRSA and VRSA were confirmed in 17.48% (25/143) and 12.58% (18/143) samples respectively. The in-vitro trials of various antibiotics for MRSA and VRSA isolates showed 100% resistance towards Cefoxitin followed by 50% towards Gentamicin, Tylosin, and Trimethoprim + Sulfamethoxazole then 25% to Oxytetracycline, and Fusidic acid while ciprofloxacin, moxifloxacin, and linezolid were found sensitive against study isolates. The public health importance of S. aureus and emerging resistance against antibiotics like methicillin and vancomycin demands regular monitoring of effective use of antimicrobial agents against the isolates of VRSA and MRSA.