Role of efflux pump inhibitors in enhancing the effect of bedaquiline on M. tuberculosis

This study investigated the effects of classical efflux pump inhibitors (EPIs) thioridazine (THZ), chlorpromazine (CPZ), verapamil (VP), and reserpine (RSP) on bedaquiline (BDQ) susceptibility in Mycobacterium tuberculosis clinical isolates explored potential interactions of these compounds with the MmpL5–MmpS5 efflux system. Twenty M. tuberculosis isolates with distinct resistance profiles and the H37Rv reference strain were evaluated using the resazurin microplate assay (REMA). BDQ minimum inhibitory concentrations (MICs) were determined alone and in combination with sub-inhibitory (½ MIC) EPI concentrations. Toxicity predictions were performed using the ProTox 3.0 platform, and molecular docking analyses were conducted via CB-Dock2 to assess ligand – protein interactions with the MmpL5–MmpS5 transporter. EPIs markedly reduced BDQ MIC values in both BDQ-susceptible and resistant isolates, with mean fold reductions of 39.66 for THZ and VP, 24.44 for CPZ, and 15.67 for RSP. Docking studies indicated higher binding affinities for THZ and RSP compared to other agents. EPIs substantially enhanced BDQ susceptibility in vitro, suggesting that efflux-mediated modulation of BDQ activity occurs. These findings provide comparative, exploratory evidence supporting EPIs as potential adjuvants and offer a reproducible experimental basis for selecting candidates for future translational and in vivo validation studies.