Dimetridazole potentiates cefotaxime against multidrug-resistant E. coli via membrane disruption and fatty acid composition.

The rising prevalence and rapid spread of multidrug-resistant bacteria have resulted in ineffective treatments, impacting millions of lives globally. In response to these challenges, drug repurposing has garnered attention as a viable alternative to traditional drug discovery and development processes. This study aimed to investigate the synergistic effects of dimetridazole and cefotaxime by evaluating their efficacy against E. coli. A checkerboard assay was performed to examine the synergy of dimetridazole in combination with cefotaxime against drug-resistant E. coli NX400. The results showed synergistic effects. Additionally, a growth curve was used to assess the growth inhibitory effects. Membrane permeability and membrane integrity were evaluated using fluorescence microscopy and scanning electron microscopy. We also analyzed the composition of membrane fatty acids and the expression of fatty acid biosynthesis-related genes. Finally, a Galleria mellonella infection model was employed to evaluate the synergistic antibacterial activity. The results showed that dimetridazole in combination with cefotaxime had significant antibacterial activity against MDR E. coli. This finding was confirmed by an in vivo G. mellonella larval infection model, in which dimetridazole revived the activity of cefotaxime. The antibacterial mechanisms are related to the bacterial membrane. Combination of dimetridazole and cefotaxime disrupts membrane integrity, permeability, and biosynthesis.