Characterization and antimicrobial resistance of Staphylococcus hyicus from swine exudative epidermitis in South Korea

Background: Staphylococcus hyicus causes porcine exudative epidermitis, predominantly affecting suckling and weaned piglets. This bacterium produces various exfoliative toxins (ExhA, ExhB, ExhC, ExhD, SHETA, and SHETB), which are responsible for the clinical manifestations of exudative epidermitis. However, treatment failure is common due to frequent antimicrobial resistance in porcine strains. Therefore, this study aimed to identify the genes encoding exfoliative toxins and assess the antimicrobial resistance profiles of S. hyicus . A total of 17 S. hyicus isolates were collected from piglets with skin lesions from 2014 to 2021. All strains were subjected to species-specific polymerase chain reaction targeting sodA to confirm the presence of S. hyicus, and polymerase chain reaction amplification of exfoliative toxin genes ( exhA , exhB , exhC , exhD , sheta , and shetb ) was performed to differentiate toxigenic strains. Pulsed-field gel electrophoresis analysis and minimum inhibitory concentration tests using broth microdilution were conducted to further analyze the strains. Results: Exfoliative toxin genes were detected in 52.9% (n = 9) of the S. hyicus isolates, with notable detection of exhB (17.6%), exhC (17.6%), exhD (11.8%), exhA (5.9%), sheta (0%), and shetb (0%). Pulsed-field gel electrophoresis analysis categorized the isolates into 11 pulsotypes with 70% similarity. Among 18 tested antimicrobials, all isolates exhibited 100% susceptibility to ceftiofur and sulfonamides and high susceptibility rates to neomycin, tilmicosin, and tetracyclines. Whereas the susceptibility rate of spectinomycin was 0% in all isolates, multidrug resistance was observed in 82.4% of the isolates, and in all toxigenic strains. Conclusions: These findings provide crucial insights for monitoring and devising effective treatment strategies for managing exudative epidermitis in pigs caused by S. hyicus .