Comprehensive analysis of antimicrobial resistance and virulence determinants in clinical methicillin-resistant...

In South Korea, studies on methicillin-resistant Staphylococcus aureus (MRSA) have predominantly focused on molecular typing, with ST5 and ST72 consistently identified as dominant lineages. However, data on the distribution of virulence factors and antimicrobial resistance genes among recent clinical MRSA isolates remain limited. This study aimed to characterize antimicrobial resistance determinants and virulence gene profiles in contemporary clinical MRSA isolates from South Korea.

One hundred human-derived clinical MRSA isolates, collected between February 2024 and January 2025 from the Antibiotic Resistance Specialized Pathogen Resource Bank of Hallym University Sacred Heart Hospital (Anyang-si, Republic of Korea), were analyzed. The isolates were evaluated for antimicrobial susceptibility and molecular characterization including multilocus sequence typing (MLST), staphylococcal cassette chromosome mec typing, accessory gene regulator grouping, staphylococcal protein A typing, and profiling of virulence and antimicrobial resistance genes. Genetic relatedness among isolates was also assessed.

The isolates demonstrated high resistance rates to penicillins, cephalosporins, fluoroquinolones, macrolides, lincosamides, and tetracyclines, whereas most remained susceptible to vancomycin, linezolid, nitrofurantoin, and trimethoprim-sulfamethoxazole. Amino acid substitutions in antimicrobial resistance-associated genes were identified in 74% of isolates, with the greatest diversity observed among ST5 strains. MLST analysis revealed that ST5 isolates harbored a broader spectrum of resistance determinants, while ST72 isolates exhibited a more limited resistance profile. PFGE identified three major clone clusters, each associated with distinct superantigen gene profile. Panton-Valentine leukocidin genes were detected exclusively in ST8 and ST22 isolates, whereas the arginine catabolic mobile element was found only in ST8 isolates.

Contemporary MRSA isolates in South Korea tested in this study share a conserved core virulence repertoire but display lineage-specific differences in resistance and virulence determinants. These findings enhance comparative molecular characterization of MRSA in South Korea and underscore the need for continued surveillance to elucidate lineage evolution and transmission dynamics.