Methicillin-resistant staphylococci isolated from healthy horses and horse personnel in Italy

Abstract

Methicillin-resistant staphylococci (MRS) were isolated from nasal swabs of 56 of 159 (35.2%; 95% confidence interval [CI]: 27.9-43.2%) healthy horses. Two nasal swabs were collected from each horse; 43 of 159 (27%; 95% CI: 20.5-34.8%) of the cohort were colonized by MRS strains in 1 nostril, while in the remaining 13 of 159 (8.2%; 95% CI: 4.6-13.9%), different or identical MRS strains were isolated in both nostrils. Of the 29 humans in close contact with the horses tested, 4 (13.8%; 95% CI: 4.5-32.6%) were found to be carriers of MRS. All isolates were coagulase negative with the exception of 2 coagulase-positive MRS strains, Staphylococcus aureus and Staphylococcus pseudintermedius, both isolated from horses. To assay the methicillin resistance, a susceptibility test to oxacillin with standardized disk diffusion method, a PBP-2a latex agglutination test, and a methicillin resistance gene (mecA) polymerase chain reaction assay were performed. Pulsed-field gel electrophoresis patterns of isolates from horses and humans in close contact with the horses revealed similarity. The results suggest evidence of transmission between animals, from animals to humans, and vice versa.