Molecular characterizations of vancomycin and methicillin-resistant Staphylococcus aureus strains isolated from intensive care unit patients in Tehran, Iran

Background: We investigated the prevalence, diversity, and antibiotic susceptibility profiles of methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant S. aureus (VRSA) strains isolated from ICU patients in Tehran, Iran.
Materials & Methods: A total of 247 S. aureus isolates were collected from patients admitted to the ICU of a referral hospital in Tehran between June and August 2022. Antimicrobial susceptibility testing was done on all isolates using the disc diffusion method. MRSA was identified by cefoxitin screening and mecA gene detection. Vancomycin resistance was assessed by E-test and confirmed by the detection of vanA and vanB genes. A combination of Staphylococcal cassette chromosome mec (SCCmec), pulsed-field gel electrophoresis (PFGE), and ccr typing methods was used to measure the genetic diversity of the strains.
Findings: Our results revealed that 60 (24%) and 7 (3%) isolates were identified as MRSA and VRSA, respectively. vanA and vanB genes were detected in 100% and 29% of VRSA isolates, respectively. There was a high level of resistance to penicillin, ciprofloxacin, and tobramycin. Out of 205 (83%) strains showing SCCmec, 96 (47%) belonged to type III SCCmec. Typing of the isolates with PFGE showed the presence of 32 pulsotypes consisting of 19 common (CTs) and 13 single types (STs) among the studied strains, with CT3 comprising 43% of VRSA strains.
Conclusion: The detection of a dominant VRSA clone and a considerable prevalence of MRSA among ICU patients underscores the role of ICUs as potential reservoirs for MRSA dissemination.