Molecular investigation and virulence determination of methicillin and vancomycin resistant clinical Staphylococcus aureus isolates

Staphylococcus aureus is an opportunistic pathogen that provides conditions for host invasion due to various virulence factors and plays a role in causing various infections. These bacteria may have different pathogenic functions depending on the susceptibility of the host. This study investigates the sensitivity of S. aureus strains isolated from clinical samples to methicillin and vancomycin and evaluates the presence of resistance, virulence and toxin-producing genes and their expression level in the methicillin-restsnat S. aureus (MRSA), vancomycin-resistant S. aureus (VRSA), and vancomycin-intermediate S. aureus (VISA) isolates. In a cross sectional study, 502 S. aureus isolates were collected from different infections during one year. Methicillin and vancomycin sensitivity of the isolates was checked by disk diffusion and microdilution broth method, respectively. The presence of resistance, adhesion, and toxin-producing genes was checked using the Multiplex PCR method. The expression level of the virulence and resistance genes was detected in resistant and sensitive isolates using real-time qPCR. Out of 502 S. aureus isolates, 168 isolates (33.6%) were MRSA. A total of 6 isolates (1.2%) were diagnosed as VRSA and two isolates (0.4%) as VISA. Virulence and resistance-related genes showed different frequencies. The results of the gene expression study showed that the expression of most of the studied genes was significantly higher in resistant isolates (MRSA and VRSA) than in sensitive isolates. VRSA and MRSA are considered severe threats to human health. The present study showed that sanitary measures are necessary to control this hospital pathogen more seriously due to the presence and expression of genes encoding virulence factors in S. aureus isolates.