Comparative Phenotypic and PCR-Based Methicillin Resistance Characterization of Clinical Canine Staphylococcus pseudintermedius

Background: Antimicrobial resistance in Staphylococcus pseudintermedius is an increasing concern in small animal medicine, particularly due to methicillin-resistant strains and associated multidrug resistance. This study aimed to characterize antimicrobial susceptibility patterns in clinical canine isolates, determine the prevalence of methicillin resistance, and assess the presence of mecA and mecC genes. Methods: A total of 243 clinical isolates from canine skin samples collected in Hungary between 2023 and 2025 were analyzed. Minimum inhibitory concentrations (MICs) for 24 antimicrobial agents were determined using broth microdilution in accordance with CLSI guidelines. Isolates were classified as methicillin-resistant or susceptible based on oxacillin MIC values. PCR assays targeting mecA and mecC were performed on oxacillin-resistant isolates. Results: Of the 243 isolates, 47 (19.3%) were methicillin-resistant. High resistance rates were observed for β-lactams, tetracyclines, macrolides, and lincosamides, while rifampicin, amikacin and florfenicol retained good to excellent activity. Methicillin-resistant isolates exhibited substantially higher resistance across multiple antimicrobial classes. Overall, 50.6% of all isolates were classified as multidrug-resistant (MDR) and 17.3% as extensively drug-resistant (XDR), while no pandrug-resistant (PDR) isolates were detected; all methicillin-resistant isolates were at least MDR. The mecA gene was detected in 80.9% of oxacillin-resistant isolates, while mecC was not identified. Conclusions: Methicillin resistance in canine S. pseudintermedius is closely associated with multidrug resistance, limiting therapeutic options. However, selected agents, including rifampicin, amikacin and florfenicol, retained in vitro activity. Partial discordance between phenotypic resistance and mecA detection highlights the importance of combined phenotypic and molecular approaches. These findings have direct implications for empirical antimicrobial therapy and support targeted treatment strategies, while emphasizing the importance of antimicrobial stewardship in small animal practice.

Authors: P. Mag, E. Fehér, E. Kaszab, D. Máté, N. Tarpataki and Á. Jerzsele Title: Comparative Phenotypic and PCR-Based Methicillin Resistance Characterization of Clinical Canine Staphylococcus pseudintermedius Full source: Antibiotics (Basel), 2026,Vol 15, Iss 5, Author keywords 15
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Background: Antimicrobial resistance in Staphylococcus pseudintermedius is an increasing concern in small animal medicine, particularly due to methicillin-resistant strains and associated multidrug resistance. This study aimed to characterize antimicrobial susceptibility patterns in clinical canine isolates, determine the prevalence of methicillin resistance, and assess the presence of mecA and mecC genes. Methods: A total of 243 clinical isolates from canine skin samples collected in Hungary between 2023 and 2025 were analyzed. Minimum inhibitory concentrations (MICs) for 24 antimicrobial agents were determined using broth microdilution in accordance with CLSI guidelines. Isolates were classified as methicillin-resistant or susceptible based on oxacillin MIC values. PCR assays targeting mecA and mecC were performed on oxacillin-resistant isolates. Results: Of the 243 isolates, 47 (19.3%) were methicillin-resistant. High resistance rates were observed for β-lactams, tetracyclines, macrolides, and lincosamides, while rifampicin, amikacin and florfenicol retained good to excellent activity. Methicillin-resistant isolates exhibited substantially higher resistance across multiple antimicrobial classes. Overall, 50.6% of all isolates were classified as multidrug-resistant (MDR) and 17.3% as extensively drug-resistant (XDR), while no pandrug-resistant (PDR) isolates were detected; all methicillin-resistant isolates were at least MDR. The mecA gene was detected in 80.9% of oxacillin-resistant isolates, while mecC was not identified. Conclusions: Methicillin resistance in canine S. pseudintermedius is closely associated with multidrug resistance, limiting therapeutic options. However, selected agents, including rifampicin, amikacin and florfenicol, retained in vitro activity. Partial discordance between phenotypic resistance and mecA detection highlights the importance of combined phenotypic and molecular approaches. These findings have direct implications for empirical antimicrobial therapy and support targeted treatment strategies, while emphasizing the importance of antimicrobial stewardship in small animal practice.