Virulence Profiling of Multidrug-Resistant Clinical Staphylococcus aureus Isolates

Staphylococcus aureus is a critical global health threat due to its multidrug resistance (MDR) and virulence. We examined the relationship between MDR and virulence in 250 clinical S. aureus isolates using the Galleria mellonella infection model. Alpha-hemolysin was the most prevalent toxin, with its gene, hla , present in the majority of hemolytic strains. Other virulence genes, including sigB, codY, fnbA, fnbB, clfA, saeS, sarA, arlS, yycG, spoVG, rot, and PVL , were widely distributed across methicillin-resistant S. aureus (MRSA) and methicillin-sensitive S. aureus (MSSA) isolates. The ica gene showed a notable increase in expression in hospital-acquired (HA-MRSA) and community-acquired (CA-MRSA) strains. In vivo infections revealed that HA-MRSA strains were more virulent than vancomycin intermediate S. aureus VISA, CA-MRSA, MSSA, and an agr mutant strain, while locally sourced CA-MRSA exhibited the highest virulence among tested strains. Despite differences in antibiotic resistance, MRSA and MSSA shared largely similar virulence gene profiles. These findings highlight the complex interplay between MDR and virulence in S. aureus and emphasize the need for further mechanistic studies. Importance: S. aureus remains a major clinical concern due to its increasing multidrug resistance (MDR) and virulence. Understanding the relationship between resistance mechanisms and virulence is essential for guiding effective treatment and infection control. This study assessed the virulence potential of 250 MDR S. aureus isolates using a clinically relevant invertebrate model ( G. mellonella ), revealing key virulence gene profiles. Notably, CA-MRSA strains exhibited hypervirulence, with alpha-hemolysin as the most prevalent toxin and significant upregulation of the ica gene in both CA- and HA-MRSA isolates. These findings emphasize the growing threat of CA-MRSA and the importance of integrated surveillance of both resistance and virulence in S. aureus populations.