Frequency and analysis of gene expression of norA and norB efflux pump in clinical isolates of Staphylococcus aureus using Ethidium bromide and Real Time PCR

Background: Ciprofloxacin resistance in Staphylococcus aureus strains due to efflux pumps has become a significant challenge. This study was performed to evaluate the frequency and gene expression of norA and norB efflux pump genes and their role in resistance to ciprofloxacin in clinical isolates of S. aureus. Methods: In this experimental study, a total of 250 clinical samples were collected from different hospitals in Tehran and S. aureus isolates were identified. Antimicrobial susceptibility patterns were determined by disk diffusion method based on CLSI standard. The presence of norA and norB efflux pump genes in ciprofloxacin isolates were detected using PCR method. Finally, active efflux pump was evaluating using MIC of ciprofloxacin-Ethidium bromide and Real Time PCR method. Results: Among 250 clinical samples, 50 S. aureus isolates were recovered and the results of antibiotic susceptibility tests show that 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% in isolates, respectively. Real Time PCR results show that more resistant strains had increased expression in norA and norB efflux genes. Conclusion: 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 suggestion of an effective treatment model for the S. aureus infections.