Berberis species derivatives potentiate the antimycobacterial activity bedaquiline, clofazimine and doxycycline against Mycobacterium smegmatis putatively via efflux inhibition

Mycobacterium tuberculosis ( Mtb ), the causative agent of tuberculosis (TB), is the leading cause of death due to a single infectious pathogen globally. The increasing prevalence of drug resistant Mtb strains underscores the pressing need for the development of new antimycobacterial drugs with novel mechanisms of action. Pathogen drug efflux is a key mechanism of antimycobacterial drug resistance. In this study, we utilised Mycobacterium. smegmatis ( Msm ), a non-pathogenic Mtb surrogate, to determine the ability of natural-product based compounds to augment the efficacy of bedaquiline (BDQ), clofazimine (CFZ) and doxycycline (DOX) by efflux inhibition (EI). Literature reporting the plant sources of the known efflux pump inhibitors (EPIs) reserpine, berberine and piperine was scoped and additional compounds isolated from the same plant species selected. In vitro screening was performed on the chosen compounds using the two-dimensional (2-D) checkerboard assay, where each putative efflux disruptor was tested in combination with BDQ, CFZ and DOX against Msm . The effect of the combinations was ascertained. Thereafter, docking of the compounds displaying probable EI activity onto Mtb MmpL5 and Rv1258c pumps was performed and revealed that majority bound with strong affinity and had docking scores of <-7kcal/mol. The combination assays revealed strong synergistic interactions when BDQ was combined with berberine (BER) and (+)-lyoniresinol-3-Alpha-O-Beta-D-glucopyranoside (LYO-3), as well as lyoniresinol (LYO), pointing to probable Msm efflux system disruption by the derivatives from Berberis species. Further examination of these putative EIs is warranted against Mtb .