Prevalence and Antimicrobial Resistance of <i>Staphylococcus aureus</i> and <i>Staphylococcus schleiferi</i> Isolated from Dogs with Otitis Externa and Healthy Dogs

Abstract

<b>Background/Objectives</b>: Antimicrobial resistance (AMR) in companion animals is a growing One Health concern due to the close interaction between pets and humans. <i>Staphylococcus aureus</i> (<i>S. aureus</i>) and <i>Staphylococcus schleiferi</i> (<i>S. schleiferi</i>) are common colonizers of the canine ear canal and can act as reservoirs of resistance. This study aimed to assess the prevalence and antimicrobial resistance profiles of <i>S. aureus</i> and <i>S. schleiferi</i> isolated from dogs with otitis externa and clinically healthy dogs in western Romania. <b>Methods</b>: A total of 973 canine ear swabs were collected, 503 from dogs with otitis externa and 470 from healthy dogs. Isolates were identified using MALDI-TOF MS. Antimicrobial susceptibility testing was performed using the VITEK^® 2 Compact system, bioMérieux, Marcy-l’Étoile, France, and interpreted according to CLSI VET01 guidelines, with 13 antimicrobials representing multiple drug classes. <b>Results</b>: <i>S. aureus</i> was more prevalent in healthy dogs (20%) than in otitis cases (4%), while <i>S. schleiferi</i> was more common in otitic samples (7.5% vs. 4%). Among <i>S. aureus</i> isolates from otitic dogs, penicillin resistance was highest (65%), and 25% were multidrug-resistant (MDR). In healthy dogs, <i>S. aureus</i> showed 54.3% penicillin resistance and 16% MDR prevalence. Four MRSA strains (4.3%) were identified only in healthy dogs. <i>S. schleiferi</i> exhibited the highest resistance to clindamycin, with MDR rates of 10.6% in otitic and 5.6% in healthy dogs. No MRSS strains were detected. <b>Conclusions</b>: Clinically healthy dogs may serve as asymptomatic carriers of resistant <i>Staphylococcus</i> strains, including MRSA. Routine antimicrobial susceptibility testing is essential to inform treatment choices and mitigate resistance dissemination within veterinary and public health contexts.