Antimicrobial Resistance and Risk Factors of Canine Bacterial Skin Infections

Bacterial skin infections are common in dogs and often secondary to underlying conditions like allergies or ectoparasite infestations. Untreated primary causes can lead to recurrent infections and an increased risk of antimicrobial resistance, including methicillin-resistant <i>Staphylococcus pseudintermedius</i> (MRSP), posing a substantial clinical challenge. Here, we analyzed 896 canine bacterial skin infection samples collected from the China Agricultural University Veterinary Teaching Hospital between 2018 and 2022. Species identification was confirmed by MALDI-TOF and 16S rRNA gene sequencing. Of the 896 samples, 722 (80.6%) yielded 1123 bacterial isolates, with <i>Staphylococcus pseudintermedius</i> (<i>n</i> = 421), <i>Pseudomonas aeruginosa</i> (<i>n</i> = 108), and <i>Escherichia coli</i> (<i>n</i> = 73) being the most prevalent. Antimicrobial susceptibility was evaluated using the broth microdilution method according to CLSI guidelines. Notably, resistance to florfenicol in <i>S. pseudintermedius</i> increased from 9.1% in 2018 to 20.0% in 2022, while resistance to ceftriaxone in <i>E. coli</i> rose from 30.0% to 72.7% over the same period. Among 305 reviewed cases, pyoderma (47.5%, 145/305) was the most common infection type, predominantly associated with <i>S. pseudintermedius</i> (<i>n</i> = 114), followed by otitis (25.6%, 78/305) primarily linked to <i>P. aeruginosa</i> (<i>n</i> = 24). Mixed infections occurred in 35.4% (108/305) of cases, with <i>S. pseudintermedius</i> as the most frequently isolated species in both single and mixed infections. The multivariable logistic regression model revealed that MRSP infections were correlated with a history of invasion (<i>p</i> <0.001) and prolonged disease duration (six months to less than one year: <i>p</i> = 0.005; one year or longer: <i>p</i> < 0.001). Core-genome SNP analysis showed that eight dogs were infected with identical <i>S. pseudintermedius</i> strains, in which one dog exhibited a shift from gentamicin susceptibility to resistance within nine days. Conversely, three dogs were infected by distinct <i>S. pseudintermedius</i> strains at two time points. To effectively manage MRSP infections and chronic skin infections in dogs, rigorous disinfection protocols in veterinary hospitals, control of disease duration, prevention of recurrent infections, and continuous monitoring of antibiotic resistance patterns are essential.