Tehran University of Medical Sciences Acta Medica Iranica 0044-6025 52 6 2014 06 15 424 429 EN Mohammad Reza Pourmand Biotechnology Research Center, Tehran University of Medical Sciences, Tehran, Iran. Masoud Yousefi Department of Pathobiology, Faculty of Public Health, Tehran University of Medical Sciences, Tehran, Iran. Seyed Alireza Salami Department of Horticulture, Faculty of Agriculture, University of Tehran, Tehran Iran. Mohsen Amini Department of Chemistry, Pharmacy and Pharmaceutical Sciences Research Center, Tehran University of Medical Sciences, Tehran, Iran. 2015 10 11 Staphylococcus aureus causes a wide variety of infections worldwide. Methicillin-resistant S. aureus is one of most common causes of nosocomial and community acquired infections. The fluoroquinolones are an important class of antibiotics that used to treat infections caused by S. aureus. Today, a significant increase in the rate of ciprofloxacin resistance in methicillin-resistant S. aureus strains is concerning. The norA efflux pump is considered as contributors to antibiotic resistance. Here, we aimed to evaluate the expression of norA efflux pump in the presence of hexahydroquinoline derivative in methicillin and ciprofloxacin resistant S. aureus. We were determined minimum inhibitory concentration of ciprofloxacin and hexahydroquinoline derivative and their combination by broth microdilution method against ciprofloxacin resistant S. aureus. The expression of the norA efflux pump gene was evaluated by quantitative Real-time PCR. This study showed that minimum inhibitory concentrations of ciprofloxacin in the presence of hexahydroquinoline derivative in comparison to ciprofloxacin were decreased. Quantitative Real-time PCR identified the increased expression of norA efflux pump gene in methicillin and ciprofloxacin resistant S. aureus strain. The increased expression of norA efflux pump gene may have resulted in the effort of S. aureus to survive. The results showed that the hexahydroquinoline derivative enhanced the antibacterial effect of ciprofloxacin against methicillin and ciprofloxacin resistant S. aureus. Therefore, the derivatives may be used as inhibitors of antibiotic resistance for combination therapy. https://acta.tums.ac.ir/index.php/acta/article/view/4785 https://acta.tums.ac.ir/index.php/acta/article/download/4785/4453