Synergistic activity of colistin in combination with resveratrol and capsaicin against mcr-1-posotive Escherichia coli

Colistin used to be regarded as the last-resort treatment for the infection caused by multidrug-resistant gram-negative bacteria. However, the emergence and widespread of mcr-1 seriously reduce the clinical effectiveness of colistin, constituting a serious threat to global public health. Due to the difficulties in the development of new antibiotics, restoring antibiotic susceptibility with adjuvants is undoubtedly a rational option. As naturally occurring compounds, resveratrol and capsaicin could be extracted from many natural plants, due to various antimicrobial properties, they have received significant attention. Herein, the synergistic activity of colistin combined with resveratrol and capsaicin against mcr-1-positive Escherichia coli were investigated by checkerboard method and time-killing assays. The in-depth molecular mechanisms were elucidated by scanning electron microscopy, fluorescent probe experiments, transcriptome and metabolome analysis. Molecular docking assay was taken to analyse potential interactions between resveratrol/capsaicin and MCR-1. Finally, the in vivo efficacy of combined therapy against mcr-1-positive Escherichia coli was assessed. Our results demonstrated that colistin combined with resveratrol and capsaicin acted synergistic activity against mcr-1-positive Escherichia coli both in vivo and in vitro. Further mechanistic studies showed that the combined therapy could exacerbate cell membrane damage, increase membrane permeability, disrupt the homeostasis of PMF, inhibit ATP synthesis, and efflux pump activity. In addition, the combined therapy could inhibit central carbon metabolism, and reduce tricarboxylic acid cycle and oxidative phosphorylation. Moreover, molecular docking assay revealed resveratrol/capsaicin could bind to MCR-1 stably. Our study indicated that colistin in combination with resveratrol and capsaicin as a novel therapy could provide a trustworthy foundation to establish the treatment plan for mcr-1-positive Escherichia coli.