TDK conference 2025

Antimicrobial resistance is one of the most serious global health challenges of our time, affecting both human and animal health. In dogs, external ear canal inflammation is one of the most common problems, often involving the bacterium Staphylococcus pseudintermedius. Our current research is investigating the antibiotic susceptibility of this pathogen.

During our study, we examined a total of 98 methicillin-sensitive Staphylococcus pseudintermedius (MSSP) and 14 methicillin-resistant Staphylococcus pseudintermedius (MRSP) isolates, and determined the minimum inhibitory concentration (MIC) using the broth microdilution method for 12 different active substances.

The sensitivity of MSSP isolates was as follows: 88.8% of strains were sensitive to amoxicillin-clavulanic acid, 90.8% to cephalexin, 92.9% to cefovecin, 78.6% to gentamicin, 90.8% to amikacin, and 95.9% to rifampicin. Only 43.9% of strains were sensitive to florfenicol, but a further 51.0% of strains were moderately sensitive. In the case of clindamycin, 36.7% of strains proved to be resistant. In the case of enrofloxacin, 59.2% of the strains were sensitive and 24.5% were moderately sensitive, while the same proportions for marbofloxacin were 39.8% and 41,8%. However, in the case of orbifloxacin, we observed 86.7% sensitivity. The MIC50 and MIC90 values for polymyxin B were 32 µg/ml and 64 µg/ml, respectively.

Of the MRSP strains, 57.1% were sensitive and 35.7% were moderately sensitive to amikacin. The same ratios were 28.6% and 57.1% for florfenicol and 85.6% and 7.2% for rifampicin. The MIC₅₀ value of the locally applicable polymyxin B active substance was 32 µg/ml, and its MIC₉₀ value was 64 µg/ml. We did not detect clinical efficacy for the other active substances.

However, our results should be evaluated in light of the fact that in most cases of external auditory canal inflammation, we use local treatment, during which high concentrations of active substances break through resistance. Systemic treatment is only necessary in complicated cases (e.g., in the presence of MRSP). In such cases, antibiotic susceptibility testing is always justified in order to avoid the selection of further resistant strains.