The NorA efflux pump considered as one of the contributors to antibiotic resistance in Staphylococcus aureus strains. One of the challenges of the researchers is finding natural plant compounds with the ability to inhibit the pumps. The aim of this study was to investigate the inhibitory effect of thyme (Thymus vulgaris) extract on NorA efflux pump in ciprofloxacin-resistant strains of S. aureus. Here, by using polymerase chain reaction (PCR), the presence of norA efflux pump was identified in 10 clinical and standard ciprofloxacin-resistant strains of S. aureus. The extract of thyme (T. vulgaris) was prepared using ethanol solvent and the effect of the extract against norA efflux pump was investigated by ethidium bromide method. In the following, after exposure to sub minimum inhibitory concentration of the extract, norA gene expression was evaluated using real-time polymerase chain reaction. Finally, we used the gas chromatography mass spectrometry (GC-mass) method to characterize the compounds with antibacterial properties. The results of PCR showed that all strains had a norA efflux pump, and ethidium bromide phenotypic method indicated that thyme extract had an inhibitory effect on all resistant strains with norA efflux pump. The norA gene expression in ciprofloxacin-resistant strains also decreased in sub minimum inhibitory concentration of the extract. By using gas chromatography- mass spectrometric, five chemical compounds of thymol, carvacrol, indole, 2-methoxy-4-methylphenol and quinic acid were determined as the dominant compounds of thyme (T. vulgaris) extract. Due to the antiefflux pump effect of thyme extract, it seems that this plant extract can be used as a good antibacterial component in the pharmaceutical industry of Iran.
