Frequencies and Antimicrobial Susceptibility of Methicillin-Resistant Staphylococcus aureus (MRSA) Isolated from Horses in South Korea

Methicillin-Resistant Staphylococcus Aureus (MRSA) has become one of the most prevalent pathogens in animals and humans giving rise to various diseases. MRSA infection in horses and transmission between horses and humans have dramatically increased recently.

This study investigated the isolation frequency and antimicrobial susceptibility of MRSA isolated from horses in South Korea.

Screening of the MRSA isolates was conducted by conventional methods and multiplex Polymerase Chain Reaction (PCR). Minimum Inhibitory Concentration (MIC) of oxacillin was determined by the broth microdilution test method. Overall antibiogram was obtained by disk diffusion susceptibility test. All antimicrobial tests were conducted in accordance with the Clinical and Laboratory Standards Institute (CLSI) guidelines.

S. aureus was isolated from 116 (19.46%) of 596 horses tested. Of the 116 S. aureus isolates, 52 (8.72%) strains were identified as MRSA by multiplex PCR. Among the 52 MRSA strains, 24 (46.15%) and 28 (53.85%) were oxacillin-resistant MRSA (OR-MRSA) and oxacillin-susceptible MRSA (OS-MRSA), respectively. OR-MRSA showed the highest susceptibility to florfenicol (100.00%), followed by doxycycline (95.83%), cefepime (91.67%), tetracycline (75.00%), and trimethoprim/sulphamethoxazole (70.83%). OS-MRSA showed the highest susceptibility to florfenicol (100.00%) and trimethoprim/sulphamethoxazole (100.00%), followed by cefoxitin (96.43%), ciprofloxacin (92.86%), enrofloxacin (92.86%), lincomycin + spectinomycin (89.29%), cefuroxime (89.29%), and cefonicid (89.29%).

This study may facilitate treatment and prevention of MRSA infections and further benefit not only horses, but also people related with horse farms, horse riding clubs and animal hospitals.