Abstract / Summary
Reduced antiseptic susceptibility mediated by multidrug efflux pumps in drug-resistant Staphylococcus aureus poses an additional infection control concern. This study investigated chlorhexidine susceptibility status and efflux pump gene distribution across different accessory gene regulator (agr) types in methicillin-resistant S. aureus (MRSA) and methicillin-susceptible S. aureus (MSSA) isolates from two major hospitals in Iran. The minimum inhibitory concentrations (MICs) of chlorhexidine against the isolates were determined. Methicillin resistance determinants, efflux pump genes, and agr types were also analysed. Furthermore, the relative expression of the mepA efflux pump gene was measured after exposure to a sub-inhibitory concentration of chlorhexidine using real-time PCR. Methicillin resistance was detected in 27.3% of isolates, and chlorhexidine MICs ranged from 0.25 to 2 mg/L. Elevated chlorhexidine MIC (≥ 1 mg/L) was observed in 33.9% of isolates and was significantly more frequent among MRSA isolates. The prevalence of sepA , mdeA , mepA , lmrS , and norA exceeded 85%, whereas qacA/B and smr were detected in 5% and 0.8% of isolates, respectively. Isolates carrying lmrS showed significantly elevated chlorhexidine MICs, and agr type III was also associated with elevated MICs. mepA expression increased significantly after exposure to a sub-MIC of chlorhexidine, with 2.158-fold and 2.729-fold increases at 30 and 60 min, respectively ( p < 0.001), and was also elevated in agr II-positive and agr III-positive isolates. Our findings reveal region-specific MRSA prevalence and reduced chlorhexidine susceptibility, suggest an association between chlorhexidine exposure and mepA overexpression, and support integrating molecular typing into surveillance of emerging resistant strains.