Resensitization of colistin-resistant bacteria by the combination of colistin and L-arginine

ABSTRACT Colistin is the last-resort antibiotic for the clinical treatment of infections caused by multidrug-resistant Gram-negative bacteria. However, the emergence of colistin-resistant bacteria, particularly those harboring the mcr-1 gene, has severely compromised the therapeutic efficacy of colistin. Herein, we demonstrated that L-arginine restores colistin susceptibility in colistin-resistant bacteria, including those with intrinsic or acquired resistance. The combination of colistin and L-arginine effectively treated murine acute peritonitis caused by a colistin-resistant bacterial infection, with no toxicity observed in either in vitro or in vivo assays. Mechanistically, we revealed that the combination enhances the permeability of the cell membrane, thereby promoting the influx of colistin, ATP efflux, and the level of reactive oxygen species (ROS), ultimately leading to the death of colistin-resistant bacteria. Furthermore, the combination downregulates membrane lipid-related genes fabZ and fadL , consequently suppressing fatty acid synthesis. This inhibition resulted in the uneven distribution of membrane lipids and lipopolysaccharide (LPS), which further increased membrane permeability. In sum, our findings indicate that the combination of colistin and L-arginine successfully reverses the colistin resistance phenotype, providing a potential therapeutic strategy to combat infections caused by colistin-resistant bacteria. IMPORTANCE The global spread of colistin-resistant bacteria has eroded one of the last lines of defense against life-threatening infections that no longer respond to conventional antibiotics. Here we show that L-arginine, a natural and safe amino acid, is an agent that can restore colistin susceptibility in strains with intrinsic or acquired resistance, and is effective in a murine peritonitis model without observable toxicity. Mechanistically, the combination increases membrane permeability and compromises the integrity of the membrane, leading to altered membrane lipid and LPS distribution that further amplifies membrane disruption. These findings establish that colistin combined with L-arginine constitutes a readily translatable therapeutic strategy to overcome colistin resistance and preserve the clinical utility of this critical last-resort antibiotic.