Antibiotic resistance assessment, and genotypic and phenotypic detection of norA efflux pump in methicillin and ciprofloxacin resistant Staphylococcus aureus isolates

Staphylococcus aureus is one of the major causes of nosocomial infections throughout the world. Efflux pumps such as norA play a major role in the development of resistance to different antibiotics in this bacteria. The aim of this study was evaluation of the antibiotic resistance and detection of efflux pump (norA) in methicillin resistant (MRSA) and ciprofloxacin resistant S. aureus isolates using genotypic and phenotypic methods.
During this sectional study, 250 clinical samples were collected from different hospitals in Tehran, Iran. S. aureus isolates were identified and the antimicrobial susceptibility patterns were determined. Ciprofloxacin minimum inhibitory concentration (MIC) was determined in both MRSA and ciprofloxacin resistant isolates. Furthermore, the presence of norA efflux pump gene in MRSA and ciprofloxacin resistant isolates was assessed phenotypically using ciprofloxacin and ethidium bromide MIC, with CCCP as efflux pump inhibitor, and genetically using PCR method.
Totally, 50 S. aureus isolates were recovered. The results of antibiotic susceptibility tests showed that 34 isolates (68%) were resistant to methicillin, of which 12 isolates (24%) were resistant to ciprofloxacin, as well. Moreover, all the MRSA- ciprofloxacin resistant strains harbored the norA gene and active efflux pump.
The results showed the correlation between ciprofloxacin resistance and norA efflux pump gene in MRSA isolates. Development of efflux pump inhibitors can be useful in the control of MRSA ciprofloxacin resistant strains.