Exploring Genomic Diversity and Phenotypic Resistance in Two Egyptian ICU-Derived Methicillin-Resistant Staphylococcus aureus Isolates Exhibiting Vancomycin Resistance.

Two health-care associated S. aureus isolates showed distinct resistance and virulence features. Isolate S1 (ST152, PVL-positive) exhibited methicillin and vancomycin resistance phenotypes without mecA/vanA/vanB, relying instead on accessory genes and efflux pumps. Isolate S2 (ST1153-MRSA) had intermediate vancomycin resistance, a complete ArlRS system, multiple virulence factors, and composite transposons, indicating hypervirulence and high adaptability. Together, these findings underscore the diverse mechanisms driving resistance and pathogenicity in S. aureus and the need for genomic surveillance in clinical settings.