Rhein reduces conjugation of IncFII-type plasmids in Escherichia coli and mitigates the spread of antibiotic resistance genes

Antibiotic resistance genes (ARGs) can be rapidly disseminated via bacterial conjugation, resulting in a substantial decline in the clinical efficacy of antibiotics. Novel therapeutic strategies independent of conventional antimicrobials are urgently needed. In this study, we identified rhein (RHE), a natural anthraquinone compound, as an effective IncFII plasmid transfer-reducing agent. At sub-inhibitory concentrations, RHE significantly reduced the conjugative transfer of IncFII plasmids in Escherichia coli . Importantly, the inhibitory effect of RHE extended to clinically relevant contexts, where it markedly impeded the transfer of the mcr-1 gene among clinical isolates and reduced plasmid dissemination in multiple organs in mouse models, demonstrating its in vivo potential. Mechanistic investigations revealed a dual mode of action that distinguishes RHE from traditional antimicrobials. Specifically, RHE compromises bacterial membrane integrity, leading to dissipation of the proton motive force and depletion of intracellular ATP, and concurrently disrupts the bacterial quorum-sensing system. Collectively, these findings establish RHE as a promising lead compound for the development of non-antibiotic therapeutics aimed at limiting the environmental and clinical spread of antimicrobial resistance. This study provides a novel and feasible strategy to address the escalating crisis of ARG transmission. IMPORTANCE Antimicrobial resistance in bacteria has become an increasingly severe global health challenge. The widespread dissemination of colistin resistance genes has markedly compromised the clinical efficacy of colistin, underscoring an urgent need for novel strategies to limit the spread of resistance determinants. In this study, we investigated the regulatory effects of rhein on IncFII-type plasmids and evaluated its intervention potential in the transmission of the colistin resistance gene mcr-1 . Our results demonstrate that RHE effectively reduces mcr-1 transfer in both in vitro and in vivo models, highlighting its potential as a promising therapeutic candidate for the prevention and control of antimicrobial resistance gene dissemination.