Repurposing fenticonazole nitrate to restore colistin susceptibility in multidrug-resistant bacteria.

Aims: To explore the synergistic effect of the combination of FN and colistin on Escherichia coli and further elucidate the mechanism of this effect.

Main Methods: Antimicrobial efficacy of the combination of fenticonazole nitrate and colistin against Escherichia coli in vitro using MIC assays, checkerboard assays, growth curves, and time-kill curves. Crystalline violet staining for detection of biofilm. Mechanisms analysis using fluorescence detection, SEM. Analysis of fenticonazole nitrate and MCR-1 interaction using molecular docking and ITC. Finally, the efficacy of combination therapy for MCR-1-positive Escherichia coli was assessed in vivo.

Key Findings: Fenticonazole nitrate significantly enhanced the ability of colistin to combat mcr-1-positive E. coli 42 in vitro. The combination could effectively inhibit biofilm formation and eradicate established biofilms. Fenticonazole nitrate and colistin could increase the outer membrane permeability of E. coli 42, disrupting the membrane potential and impairing PMF synthesis, which in turn led to a reduction in ATP levels and cell death. Further, we found that the outer membrane barrier of Gram-negative bacteria and the innate resistance mechanism mediated by efflux pumps can impair the antimicrobial activity of fenticonazole nitrate. Finally, the combination demonstrated strong synergistic effects in a mouse model of infection with mcr-1-positive E. coli 42. Compared to the colistin only group, the survival rate increased by 40 %.

Conclusion: Fenticonazole nitrate is a promising antibiotic adjuvant against infections caused by MCR-1-positive multidrug-resistant pathogens.