Identification of norA, qacAB and smr genes and determination of antibiotic and biocide resistance patterns in methicillin-resistant Staphylococcus aureus isolated from Isfahan-Iran

Abstract

Background: Methicillin-resistant Staphylococcus aureus (MRSA) is a major cause of nosocomial infections, which have become a serious problem due to antibiotic resistance. In addition to antibiotic resistance, biocide resistance is also increasing due to the high use of these substances. The aim of this study was to investigate the pattern of antibiotic resistance and the prevalence of biocide resistance genes norA, qacA/B and smr, and to determine the minimum inhibitory concentration of chlorhexidine digluconate (CHG) and benzalkonium chloride (BKC) in MRSA isolates taken from teaching hospitals in Isfahan city, Iran. Materials and Methods: This study was conducted on 63 MRSA isolates collected from teaching hospitals in Isfahan city, Iran. MRSA isolates were identified by performing phenotypic testing and then confirmed by using PCR. The resistance pattern was determined by using disc diffusion method. Broth microdilution method was performed to determine the minimum inhibitory concentration (MIC) of CHG and BKC according to the Clinical and Laboratory Standards Institute (CLSI). The presence of biocide resistance genes was determined by using PCR and the Time kill assay was performed to investigate the lethality of biocides. Results: MRSA isolates had MIC values of 0.5–4 μg/ml for BKC and 0.125–4 μg/ml for CHG. norA was the most common biocide resistance gene among 63 isolates (88.9%), followed by qacAB and smr with 28.6% and 22.2%, respectively. Among the isolates, the highest percentage of resistance belonged to penicillin, erythromycin and doxycycline, respectively. Conclusion: Due to the high prevalence of MRSA isolates in hospitals and the role of this pathogen in nosocomial infections, continuous monitoring of antimicrobial resistance for appropriate antibiotic administration and continuous evaluation of biocide resistance due to the high prevalence of resistance genes and appropriate use of biocides for disinfection, allows us to minimize further prevalence of resistant strains in hospital environments.