FC‐46 Methicillin‐resistant Staphylococcus intermedius organisms from the vertical ear canal of dogs with end‐stage otitis externa

Abstract

Methicillin‐resistant staphylococci (MRS) have been isolated from the ears of dogs with otitis externa; however, the specific location of the sample and the condition of the ear were not disclosed. The purpose of this study was to identify MRS from the vertical ear canal in dogs with end‐stage otitis externa. Swab samples were obtained from one vertical ear canal of 26 dogs undergoing a total ear canal ablation and bulla osteotomy. Swab samples were routinely processed for bacterial culture. No topical or oral antimicrobial agents had been administered within 24 h of obtaining the sample. Testing for oxacillin (methicillin) resistance was performed with the disk diffusion test (DD) and confirmed with the oxacillin screen agar test (OSA) for staphylococcal organisms. Twenty‐three staphylococcal organisms [21 Staphylococcus intermedius (SI), 2 coagulase‐negative staphylococci (CNS)] were isolated from 17 dogs. On the DD, 15 organisms were susceptible (13 SI, two CNS), one was intermediate (SI), and seven were resistant (all SI) to methicillin. On the OSA, one SI that was intermediate on DD was susceptible, and of the seven that were resistant on DD, five SI were susceptible and two SI were resistant to methicillin. Both methicillin‐resistant S. intermedius (MRSI) were susceptible to chloramphenicol, polymyxin B and trimethoprim‐sulfadiazine. In dogs with end‐stage otitis externa, MRSI may be an important pathogen. Had OSA not been performed to confirm MRS, five of seven staphylococcal organisms would have been erroneously reported as resistant to certain antibiotics, which may have affected antibiotic selection and treatment of the otitis. Funding: Bayer Animal Health, The Ohio State University Canine Research Fund, American College of Veterinary Dermatology, Ohio Animal Health Foundation.