Synergistic effect of Zataria multiflora and Lavandula stoechas essential oils on phenotype detection of efflux pump against multidrug-resistant Acinetobacter baumannii isolates

Abstract

Background: Acinetobacter baumannii infections have become a major cause of hospital-acquired infections worldwide and can rapidly develop resistance to antibiotics. There are various mechanisms for multidrug resistance in the A. baumannii and efflux pumps is the most important among those. The purpose of this study is to evaluate the synergistic effect of Zataria multiflora and Lavandula stoechas essential oils on phenotype detection of efflux pump against multidrug-resistant A. baumannii isolates. Methods: A total of 55 A. baumannii strains were collected from clinical specimens and those with multidrug resistant (MDR) has been isolated by using the Kirby-Bauer disk diffusion method. Z. multiflora and L. stoechas essential oils were extracted and analyzed by gas chromatography–mass spectrometry. The minimum inhibitory concentration for antimicrobial activity of essential oils against MDR A. baumannii strains and fractional inhibitory concentration index was evaluated to determine their synergistic effect. The activity of efflux pumps of MDR strains was investigated by the ethidium bromide-agar cartwheel method and the inhibitory effect of essential oils on the efflux pumps activity was evaluated. Results: The results of this study showed that Z. multiflora and L. stoechas essential oils had additive antibacterial effects against MDR A. baumannii strains. The study of efflux pumps by cartwheel method showed that 10% of the strains had active efflux pump, after the effect of 1/2 minimum inhibitory concentration synergistic of Z. multiflora and L. stoechas essential oils, the activity of efflux pumps was inhibited. Conclusion: The combination of Z. multiflora and L. stoechas essential oils against MDR A. baumannii strains were additive antibacterial effects. It was also found that these compounds, as inhibitors of efflux pumps, could also be used to suppress MDR A. baumannii isolated.