Antimicrobial Resistance Profile of Staphylococcus pseudintermedius Isolated from Dogs with Otitis Externa and Healthy Dogs: Veterinary and Zoonotic Implications

Background/Objectives: Staphylococcus pseudintermedius (S. pseudintermedius) is an opportunistic pathogen frequently isolated from dogs, involved in a wide range of infections, particularly otitis externa. Increasing antimicrobial resistance (AMR), including methicillin-resistant S. pseudintermedius (MRSP), poses significant challenges for veterinary and potentially human health. This study aimed to assess the prevalence and antimicrobial resistance profiles of S. pseudintermedius in dogs with otitis externa compared to clinically healthy dogs. Methods: Between 2022 and 2025, samples were collected from 400 dogs with otitis externa and 360 healthy dogs in veterinary clinics from Timișoara. Ear swabs were processed by conventional microbiological techniques and confirmed using MALDI-TOF MS. Antimicrobial susceptibility was tested using the VITEK® 2 Compact system, following CLSI VET01, Fifth Edition (2018) standards. Fourteen antimicrobials from 11 classes were evaluated. Results: S. pseudintermedius was isolated in 40% of dogs with otitis externa and in 21.1% of healthy dogs. The highest resistance in both groups was observed to tetracycline (37.5% and 25%, respectively). No resistance was recorded to linezolid, vancomycin, teicoplanin, tigecycline, or fusidic acid. MRSP strains were identified in 1.2% of dogs with otitis, displaying multidrug resistance (MDR). MDR strains were also detected in 8.7% of diseased and 4% of healthy dogs, indicating the potential for subclinical reservoirs. Conclusions: The findings highlight the notable prevalence and AMR of S. pseudintermedius in both symptomatic and asymptomatic dogs. The detection of MRSP and MDR strains emphasizes the need for prudent antibiotic use and continuous AMR surveillance in veterinary medicine to mitigate zoonotic risks and preserve antimicrobial efficacy.