Inhibitory effect of menthol and thymol on MexCD-OprJ efflux pump of Pseudomonas aeruginosa under In-vitro and In-silico conditions

BACKGROUND AND OBJECTIVESMany studies have documented the inhibitory influence of bioactive compounds of herbal origins on efflux pumps in antibiotic-resistant bacteria. Here, the efficacy of menthol and thymol, as two natural derivatives, was investigated against four strains of Pseudomonas aeruginosa using in-silico molecular docking and ethidium bromide-agar cartwheel methods.MATERIALS AND METHODSSerial two-fold dilutions were prepared in tubes assigned to each herbal compound (menthol and thymol) and bacterial strain. The sub-MIC values were calculated after culturing the bacteria on Mueller-Hinton agar (MHA). Subsequently, the cartwheel test (for the strains, with and without exposure to menthol and thymol) was carried out on MHA media containing ethidium bromide and then the plates were observed in a UV transilluminator. Turning to the in-silico study, the three-dimensional structures of menthol and thymol as the ligands and MexCD-OprJ protein as the pump receptor were obtained from PubChem and protein databases, correspondingly, and were evaluated in molecular docking using Autodock (version ۴.۱).RESULTS AND DISCUSSIONThe cartwheel method demonstrated reduced pump activity in all strains grown under sub-MIC values of the bioactive compounds, which displayed the red color of ethidium bromide under UV light. It was found that menthol has a higher inhibitory potential and shows greater binding energy (ΔG= -۵.۸۱ Kcal.mol-۱) with MexCD-OprJ protein compared to thymol (ΔG= -۵.۶۳ Kcal.mol-۱). Menthol only interacts with amino acids serine B:۵۷ and glutamine B:۶۰, while thymol is able to interact with glycine A:۳۰۳, serine A:۳۰۵, threonine A:۳۰۴, serine A: ۳۱۹, tryptophan A:۳۲۰, glutamine A:۱۱۱, serine A:۳۰۱, threonine A:۸۸, alanine A:۸۶, alanine A:۱۱۵, glycine A:۱۱۳, leucine A:۱۱۴, phenylalanine A:۳۰۲, and valine A: ۱۱۲.CONCLUSIONThese results suggest that menthol and thymol can be proposed as potential inhibitory agents against various strains of Pseudomonas aeruginosa.

کلیدواژه ها:

Cartwheel method ، Menthol ، MexCD-OprJ Efflux pump ، Molecular docking ، Pseudomonas aeruginosa ، Thymol