Prevalence and risk factors for isolation of methicillin-resistant Staphylococcus in dogs with keratitis

To determine the prevalence of, and risk factors for, methicillin-resistant Staphylococcus (MRS) isolation in dogs with naturally acquired bacterial keratitis.

All Staphylococcus spp. isolated from corneal samples of dogs with keratitis during a 2-year period were evaluated for methicillin resistance by bacteriologic methods. Each MRS isolate was subjected to in vitro susceptibility testing for systemic and ocular antimicrobials. Nasal swabs for culture were collected from all dogs with MRS corneal isolation to evaluate for nasal carrier status. Potential risk factors for MRS isolation were investigated by medical record review and administration of an epidemiological survey to dog owners. Collected information characterizing animal, client, and environmental variables was analyzed for association with MRS isolation.

Seventy-one Staphylococcus spp. were isolated from seventy individual dogs with keratitis during the study period. Seventeen of the Staphylococcus isolates (23.9%) were methicillin resistant. The MRS isolates included Staphylococcus epidermidis (n = 10), Staphylococcus pseudintermedius (n = 6), and Staphylococcus aureus (n = 1). The MRS corneal isolates displayed extensive antimicrobial resistance. Four dogs (23.5%) with MRS corneal isolates had positive nasal cultures for MRS. Client occupation was significantly (P = 0.01) associated with MRS isolation, and dogs belonging to owners employed in veterinary or human healthcare fields were four times more likely to have MRS keratitis than dogs owned by clients with different professions. There were no significant associations between the other evaluated animal, client, and environmental factors.

Methicillin resistance is relatively common in Staphylococcus isolates from dogs with corneal infections, particularly among dogs belonging to healthcare workers.