Prevalence and risk factors for colonization with methicillin resistant Staphylococcus aureus and other Staphylococci species in hospitalized and farm horses in Israel.

Methicillin-resistant staphylococci (MRS), and specifically Methicillin-resistant Staphylococcus aureus (MRSA) colonization or infection have become a serious emerging condition in equine hospitals, with complex concerns regarding animals, personnel and public health. The objectives of this study were to evaluate the prevalence and risk factors for colonization by Staphylococci, MRS, and MRSA among horses in Israel. Nasal swabs were collected from horses at 17 riding stables (n=206), and from hospitalized horses admitted to a veterinary hospital (n=84). Species identification was performed by pta gene PCR, RFLP analysis and sequencing. MRS was identified by the presence of mecA. Genetic relatedness of MRSA isolates was determined by spa typing and MLST. SCCmec-type and pvl gene were determined. Univariable and multivariable statistical analysis were used to identify potential risk factors. Colonization with Staphylococci was found among 3.8% of farm horses and 50.6% of hospitalized horses (p<0.05). MRS isolates were not found in any of the farm horses, but were isolated from 21.6% of the horses at the veterinary hospital, comprising 42.8% of all hospital isolates. MRSA was found exclusively among hospitalized horses (7.2%). All MRSA isolates belonged to a unique single multi-drug-resistant clone, ST5-SCCmec V, pvl-negative, spa-type t535. Risk factors for colonization with MRS were pure bred, hospitalization and antibiotic use. This is the first surveillance study of Staphylococci in horses in Israel, and the first report on the presence of a unique MRSA strain among hospital horses, recognizing the veterinary hospital as a potential reservoir for MRSA, an antibiotic resistant pathogen with human relevance.