Vetnuus | December 2025 7 Leading Article The objectives of this study were to determine the prevalence of S. pseudintermedius in dogs with otitis externa compared to clinically healthy dogs, to characterise the antimicrobial resistance profiles of the isolates against both veterinary and human-use antibiotics, to identify MRSP and MDR strains, and to assess their potential zoonotic implications. These aims were designed to provide a clearer understanding of the epidemiological role of S. pseudintermedius in canine populations and to support strategies for prudent antimicrobial use in veterinary medicine. 2. Results 2.1 Prevalence of S. pseudintermedius Isolated from Dogs with Otitis Externa and from the Ears of Healthy Dogs. Out of 400 samples collected from dogs diagnosed with otitis externa, S. pseudintermedius was isolated in 160 cases, representing a prevalence rate of 40%. From the ears of clinically healthy dogs, the bacterium was identified in 76 out of 360 samples, corresponding to a prevalence of 21.1%. 2.2 Antimicrobial Resistance of S. pseudintermedius Strains Isolated from Dogs with Otitis Externa. Among dogs with otitis externa, S. pseudintermedius showed the highest resistance to tetracycline (37.5%, n = 60). No resistance was observed to linezolid, teicoplanin, vancomycin, fusidic acid, and tigecycline, with 100% susceptibility (n = 160) (Table 1). Antimicrobial Class Antimicrobial Number of Strains Tested Susceptible, n (%) Resistant, n (%) Beta-lactams Penicillin 160 123 (80.3) 37 (19.7) Oxacillin 160 158 (98.7) 2 (1.3) Aminoglycosides Gentamicin 160 158 (98.7) 2 (1.3) Tetracyclines Tetracycline 160 100 (62.5) 60 (37.5) Fluoroquinolones Ciprofloxacin 160 158 (98.7) 2 (1.3) Moxifloxacin 160 158 (98.7) 2 (1.3) Macrolides Erythromycin 160 158 (98.7) 2 (1.3) Lincosamides Clindamycin 160 125 (78.1) 35 (21.9) Oxazolidinones Linezolid 160 160 (100) 0 (0) Glycopeptides Teicoplanin 160 160 (100) 0 (0) Vancomycin 160 160 (100) 0 (0) Fusidans Fusidic acid 160 160 (100) 0 (0) Glycylcyclines Tigecycline 160 160 (100) 0 (0) Sulfonamides + Pyrimidines Trimethoprim + Sulfamethoxazole 160 154 6.2) 6(3.8) Table 1. Antimicrobial resistance of S. pseudintermedius strains isolated from dogs with otitis externa 2.3 Antimicrobial Resistance of S. pseudintermedius Strains Isolated from the Ears of Healthy Dogs. Additionally, S. pseudintermedius isolated from samples collected from the ears of healthy dogs exhibited the highest resistance to tetracycline as well, at a rate of 25% (n = 19) (Table 2). Antimicrobial Class Antimicrobial Number of Strains Tested Susceptible, n (%) Resistant, n (%) Beta-lactams Penicillin 76 61 (80.3) 15 (19.7) Oxacillin 76 76 (100) 0 (0) Aminoglycosides Gentamicin 76 76 (100) 0 (0) Tetracyclines Tetracycline 76 57 (75) 19 (25) Fluoroquinolones Ciprofloxacin 76 76 (100) 0 (0) Moxifloxacin 76 76 (100) 0 (0) Macrolides Erythromycin 76 76 (100) 0 (0) Lincosamides Clindamycin 76 59 (77.6) 17 (22.4) Oxazolidinones Linezolid 76 76 (100) 0 (0) Glycopeptides Teicoplanin 76 76 (100) 0 (0) Vancomycin 76 76 (100) 0 (0) Fusidans Fusidic acid 76 76 (100) 0 (0) Glycylcyclines Tigecycline 76 76 (100) 0 (0) Sulfonamides + Pyrimidines Trimethoprim + Sulfamethoxazole 76 76 (100) 0 (0) Table 2. Antimicrobial resistance of S. pseudintermedius strains isolated from the ears of healthy dogs
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