Characterization of Virulence Genes and Antibiotic Resistance of Methicillin-resistant Staphylococcus aureus (MRSA) and Methicillin-susceptible Staphylococcus aureus (MSSA) Isolates in Intensive Care Unit (ICU) and Non-ICU Wards

Abstract

Background: We are witnessing the increasing use of antibiotics and the upward trend of resistant nosocomial infections. Therefore, identifying pathogens and determining the local patterns of antibiotic resistance are the health system's priorities in any region. Objectives: The current study aimed to investigate the prevalence of methicillin-resistant Staphylococcus aureus (MRSA) in the Intensive Care Unit (ICU) and Non-ICU wards, the toxic shock syndrome toxin-1 (TSST-1), alpha-toxin (Hla), and pantone-valentine leucocidin (PVL) genes in S. aureus strains, and antibiotic resistance patterns to provide a clinical guide for clinicians in Southwest Iran. Methods: Staphylococcus aureus was isolated from clinical specimens between 2018 and 2020. Methicillin-resistant S. aureus was detected by cefoxitin screening. Then, the antimicrobial resistance of all isolates was tested with the disk diffusion (DD) and the minimum inhibitory concentration (MIC) methods. Virulence genes, including TSST-1, Hla, and PVL, were evaluated by the PCR method. Results: Of 186 S. aureus strains isolated from various specimens, 51 (27.4%) were MRSA, with a 26.8% rate in the ICU. All isolates were susceptible to vancomycin, teicoplanin, linezolid, daptomycin, and quinupristin-dalfopristin. The penicillin-resistant S. aureus proportion was 93.5% (174/186), and more than 50% of all S. aureus isolates were resistant to fluoroquinolones. The incidence rates of virulence factors, including TSST-1, Hla, and PVL genes in MRSA, were 3.9%, 39.2%, and 2%, respectively. Conclusions: It is recommended to start empiric treatment against MRSA in case of severe infections in the ICU with either quinupristin-dalfopristin, daptomycin, vancomycin, teicoplanin, or linezolid until the culture and antibiotic susceptibility test results are available. Nevertheless, following the antibiotic resistance pattern is necessary to start treatment for other infections.