A comparative evaluation of methicillin-resistant staphylococci isolated from harness racing-horses, breeding mares and riding-horses in Italy

To investigate the prevalence of methicillin-resistant staphylococci (MRS) which is a potencial risk factor of transmission between animals and humans in different types of horses (harness racing-horses, breeding mares and riding-horses) and to compare the antimicrobial resistance of the isolates. A total of 191 healthy horses, housed at different locations of the Campania Region (Italy), were included in the study. Nasal swab samples were collected from each nostril of the horses. The mecA gene was detected by a nested PCR technique. Antibiotic susceptibility testing was performed for each isolate. MRS were isolated from nasal samples of 68/191 (35.6%; 95% CI: 28.9%-42.9%) healthy horses. All isolates were coagulasenegative with the exception of two coagulase-positive-MRS strains, identified as Staphylococcus aureus and Staphylococcus pseudintermedius, 2/83 (2.4%; 95% CI: 0.4%-9.2%). Interestingly, both coagulase-positive-MRS isolates were from harness racing-horses. These horses also presented a significant higher positivity for MRS (53.3%; 95% CI: 40.1%-66.1%) than the breeding mares and riding-horses groups. Antibiotic susceptibility testing resulted difference between isolates due to different origin except for an almost common high resistance to aminopenicillins, as ampicillin and amoxicillin. It can be concluded that harness racing-horses may act as a significant reservoir of MRS as compared to breeding mares and riding-horses.