Mechanism of synergistic action of colistin with resveratrol and baicalin against mcr-1-positive Escherichia coli

The rising incidence of colistin (COL) resistance poses a significant challenge, undermining the therapeutic efficacy of COL against life-threatening bacterial infections. Therefore, the urgent identification and development of new therapeutics are imperative. It has been proven that combinations of antibiotics and promising non-antibiotic agents could be a potential strategy to combat infections caused by MDR pathogens. Due to various antimicrobial properties, medicinal plants have attracted significant attention, which could be promising adjuvant. In this study, we investigated the synergistic effects of combining COL with resveratrol (RST) and baicalin (BAI) against mcr-1-positive Escherichia coli through antibiotic susceptibility testing, checkerboard method and time-killing assays. The mechanisms of combination treatment were analyzed using SEM, fluorometric assays and transcriptome analysis. The molecular docking assay was conducted to elucidate potential interactions between RST, BAI and the MCR-1 protein. Finally, we assessed the in vivo efficacy of combination against mcr-1-positive Escherichia coli. The results demonstrated that the combination of RST, BAI and COL showed significant synergistic activity both in vitro and in vivo. Further mechanistic study revealed that the combination could increase the membrane-damaging ability of COL, disrupt the homeostasis of proton motive force (PMF), inhibit the activity of efflux pumps and impair ATP supply. The molecular docking revealed that RST and BAI could bind to MCR-1 stably, indicating the combination of RST and BAI may be an effective MCR-1 inhibitor. Our findings demonstrated that the combination of RST and BAI might be potential COL adjuvant, providing an alternative approach to address mcr-1-positive Escherichia coli infections.