BACKGROUND AND OBJECTIVE: The existence of efflux pumps such as norA is one the mechanisms of resistance to antibiotics like ciprofloxacin in staphylococcus aureus bacteria. NorA efflux pump and its gene expression and activity in ciprofloxacin resistant S. aureus strains are investigated in this study.

METHODS: In this experimental study, 250 clinical samples of blood, urine, wound and trachea were collected from patients hospitalized in various hospitals of Tehran. S. aureus isolates were detected and thereafter, antibiotic resistance profile, gene expression of norA efflux pump and its existence were investigated using PCR and Real-Time PCR and the activity of norA efflux pump was investigated using minimum inhibitory concentration (MIC).

FINDINGS: Of 250 clinical samples, 50 S. aureus isolates were detected and the antibiotic susceptibility test results revealed that 68% of samples (34 samples) were resistant to methicillin and 32% of samples (16 samples) were susceptible to methicillin and 24% of all samples (12 samples) were resistant to ciprofloxacin. Real-Time PCR test results revealed that each type of strain has a different expression of norA gene and more resistant strains have increased expression of norA gene. Moreover, all ciprofloxacin resistant strains had active efflux pump.

CONCLUSION: The results of the study demonstrated that there is a significant relationship between gene expression of norA efflux pump, its activity and resistance to ciprofloxacin in S. aureus strains