Prevalence of norA and norB efflux pump genes in clinical isolates of Staphylococcus aureus and their contribution in ciprofloxacin resistance

Recently, ciprofloxacin resistance in Staphylococcus aureus strains due to efflux pumps has become a significant challenge. This study was performed to evaluate the frequency of norA and norB efflux pump genes and their roles in resistance to ciprofloxacin in clinical isolates of S. aureus.
A total of 250 clinical samples were collected from different hospitals Tehran-Iran during 2015-2016 and S. aureus isolates were identified by standard microbiological tests. Antimicrobial susceptibility patterns were determined by disk diffusion method using CLSI guideline. Subsequently, the presence of norA and norB efflux pump genes in ciprofloxacin isolates were detected using PCR method. Finally, active efflux pumps were evaluated using ciprofloxacin and ethidium bromide MICs.
Among 250 clinical samples, 50 S. aureus isolates were recovered and the results of antibiotic susceptibility tests showed the 34 out of 50 S. aureus isolates (68%) were resistant to methicillin (MRSA) and from the 34 MRSA, 12 isolates (24%) were resistant to ciprofloxacin. Moreover, the norA and norB genes were found in 100% and 83% of ciprofloxacin resistant isolates, respectively.
The results of this study show the potential role played by norA and norB efflux pumps in the development of resistance to ciprofloxacin in clinical isolates of S. aureus and the detection of these genes could be important for the suggestion of an effective treatment model for the S. aureus infections.