Resistance to antibiotics and biocides and prevalence of qacAB, smr and norA genes in vancomycin-resistant Enterococci isolated from patients of medical education centers in Isfahan, Iran

Vancomycin-resistant Enterococci (VRE) are one of the most common hospital pathogens due to antibiotic and biocide resistance, which has become of the major problems in hospitals. This study was conducted in order to determine the pattern of antibiotic resistance, the minimum inhibitory concentration of chlorhexidine and benzalkonium chloride, to investigate the prevalence of biocide resistance genes norA, smr and qacAB and to measure the time-kill assay of biocides in VRE isolates.

In this study, 50 isolates of VRE were collected from teaching hospitals in Isfahan and confirmed by microbiological testing. Antibiotic susceptibility was determined by disk diffusion method and the minimum inhibitory concentration (MIC) of benzalkonium chloride and chlorhexidine was determined by broth microdilution method. Prevalence of biocide resistance genes and determining the killing power of biocides were investigated by PCR and time-kill assay respectively.

Among 50 clinical isolates, all isolates were resistant to ciprofloxacin and erythromycin and susceptible to linezolid. We reported the MIC range of benzalkonium chloride and chlorhexidine 4-8 μg/ml and 1-8 μg/ml respectively. The frequency of norA, smr and qacAB genes were 84%, 56% and 24%.

The results of the present study showed that in addition to linezolid as the drug of choice for vancomycin-resistant isolates, the biocides chlorhexidine and benzalkonium chloride also had a very good lethal effect on these isolates. But due to the high resistance to other antibiotics, it seems necessary to do an antibiotic sensitivity test.