Deciphering the Antibacterial Mechanisms of 5-Fluorouracil in Escherichia coli through Biochemical and Transcriptomic Analyses

The emergence of carbapenem-resistant Gram-negative pathogens presents a clinical challenge in infection treatment, prompting the repurposing of existing drugs as an essential strategy to address this crisis. Although the anticancer drug 5-fluorouracil (5-FU) has been recognized for its antibacterial properties, its mechanisms are not fully understood. Here, we found that the minimal inhibitory concentration (MIC) of 5-FU againstEscherichia coliwas 32–64 µg/mL, including strains carryingblaNDM-5, which confers resistance to carbapenems. We further elucidated the antibacterial mechanism of 5-FU againstE. coliby using genetic and biochemical analyses. We revealed that the mutation of uracil phosphoribosyltransferase-encoding geneuppincreased the MIC of 5-FU againstE. coliby 32-fold, indicating the role of theuppgene in 5-FU resistance. Additionally, transcriptomic analysis ofE. colitreated with 5-FU at 8 µg/mL and 32 µg/mL identified 602 and 1082 differentially expressed genes involved in carbon and nucleic acid metabolism, DNA replication, and repair pathways. The biochemical assays showed that 5-FU induced bacterial DNA damage, significantly increased intracellular ATP levels and the NAD+/NADH ratio, and promoted reactive oxygen species (ROS) production. These findings suggested that 5-FU may exert antibacterial effects onE. colithrough multiple pathways, laying the groundwork for its further development as a therapeutic candidate against carbapenem-resistant bacterial infections.