Abstract

Background: Efflux pumps such as MexEF-OprN and mexXYOprM play an important role in the resistance of Pseudomonas aeruginosa (P. aeruginosa) to antibiotics. The present study aimed to assess the reduced expression of efflux pump genes of P. aeruginosa with Satureja khuzistanica essential oil (SKEO). Methods: The present cross-sectional study was conducted in 2016 at the Microbiology Laboratory of Baqiyatallah University of Medical Sciences, Tehran, Iran. The disk diffusion method was used for susceptibility testing of gentamicin and norfloxacin. Minimum inhibitory concentration (MIC) was determined for gentamicin and norfloxacin. The antibacterial efficacy of SKEO was defined by determining the MIC values using the microdilution method. In vitro, the synergistic interaction of SKEO combined with gentamicin or norfloxacin was examined via checkerboard assay and defined as a fractional inhibitory concentration index. The reverse transcription-polymerase chain reaction technique was used to measure changes in the expression of the efflux pump genes. The data were analyzed using SPSS software version 16.0, and P<0.05 was considered statistically significant. Results: The MIC values of SKEO were in the range of 6 to 12 mu g/mL. In the presence of sub-inhibitory concentrations (1.16 to 2 MIC) of SKEO, synergistic effects were revealed using the checkerboard method. The effect of norfloxacin and gentamicin increased up to 8-fold. The expression of mexY and mexE was reduced after treatment with SKEO. Conclusion: SKEO reduced the expression of efflux pumps and the MIC values of norfloxacin and gentamicin in vitro.