Detection of efflux pump activity and gene expression among ciprofloxacin-resistant Staphylococcus aureus strains

Staphylococcus aureus is one of the important nosocomial infection agents. Recently, S. aureus strains have become resistant to ciprofloxacin and the efflux pump is considered as its contributor. Herein, we investigated the presence, expression, and activity of efflux pump genes (norA and norB) among ciprofloxacin-resistant S. aureus isolates.

A total of 250 clinical samples were subjected to isolation of S. aureus strains. The antibiotic resistance pattern was characterized and the presence and expression level of norA and norB genes was assessed using PCR test and real-time PCR test, respectively. Finally, active efflux pumps were detected in ciprofloxacin-resistant S. aureus strains using the ethidium bromide test.

Among total clinical samples, 50 S. aureus strains were recovered. Of this 12 samples (24%) were resistant to ciprofloxacin. Moreover, norA and norB genes were found in 100 % and 83% of ciprofloxacin-resistant isolates, respectively. All ciprofloxacin-resistant isolates exhibited active efflux pumps. Real-time PCR results revealed that the isolates are more resistant to ciprofloxacin having a high level of efflux pump gene expression.

The results of this study showed that norA and norB efflux pump genes play an important role in resistance to ciprofloxacin in S. aureus strains.