Antimicrobial resistance and chlorhexidine susceptibility in canine staphylococcal isolates from dogs with pyoderma...

Staphylococci, particularly Staphylococcus pseudintermedius, are the major pathogens of canine pyoderma. Meanwhile, the emergence of antimicrobial resistance has become a global concern. Chlorhexidine digluconate is widely used antiseptic in veterinary medicine; however, recent studies on chlorhexidine susceptibility in veterinary staphylococci remain limited. This study evaluated the antimicrobial resistance, chlorhexidine digluconate susceptibility, and presence of antiseptic resistance-associated genes (qacA/B, qacG, and smr) in staphylococcal isolates from dogs with pyoderma and clinically healthy dogs in Korea. In total, 145 staphylococcal isolates were obtained, including S. pseudintermedius and S. schleiferi. Antimicrobial susceptibility was evaluated using the disk diffusion. Chlorhexidine digluconate susceptibility was determined using the microdilution, qacA/B and smr were detected using real-time PCR, and qacG was detected using conventional PCR. Of the 145 isolates, 93 (64.1%) were classified as multidrug-resistant (MDR). Chlorhexidine digluconate minimum inhibitory concentrations (MICs) ranged from 0.25 to 2 μg/mL, with no significant difference between MDR and non-MDR isolates. qacA/B, qacG, and smr were detected in 4, 13, and 10 isolates, respectively. Isolates carrying both qacA/B and smr showed relatively higher MICs; however, the number of positive isolates was small, and single-gene carriage was not clearly associated with increased MICs. Overall, the chlorhexidine digluconate MICs were substantially lower than the clinical concentrations, and antiseptic resistance-associated genes were detected at low frequencies. Despite the high frequency of MDR isolates, chlorhexidine digluconate remains a useful antiseptic option, although continuous monitoring of reduced susceptibility and antiseptic resistance-associated genes is warranted.