Mechanism of Synergistic Action of Isochlorogenic Acid C and Ciprofloxacin Against Drug-Resistant Escherichia coli.

BACKGROUND: The rapid emergence of antibiotic resistance in E. coli has outpaced the development of new drugs, creating an urgent demand for novel therapeutic strategies. METHODS: We screened ten antibiotics in combination with isochlorogenic acid C (ICAC) against multidrug-resistant (MDR) E. coli. Synergistic effects of antibiotics and ICAC were evaluated by measuring the leakage of alkaline phosphatase (AKP), potassium ions (K+), as well as changes in total protein, and ATP levels. The integrity of bacterial membrane and cell wall was visualized by SEM and CLSM. The underlying mechanisms were elucidated via proteomic analysis and molecular docking. Finally, the protective effect of ICAC in vivo was evaluated using an intraperitoneal infection model in SPF female BALB/c mice. RESULTS: ICAC exerted a specific synergistic effect with ciprofloxacin, significantly enhancing its efficacy. The combination disrupted bacterial membrane and cell wall integrity, increased permeability, and inhibited ATP synthesis. Mechanistically, ICAC may target OmpF and inhibit fatty acid biosynthesis. This interference reduced β-oxidation and the influx of acetyl-CoA into the TCA cycle, thereby impairing bacterial energy metabolism and destabilizing the membrane. In vivo validation using a mouse peritonitis model confirmed that the combination treatment effectively alleviated systemic E. coli infection. CONCLUSION: ICAC may potentiate the antibacterial activity of ciprofloxacin through targeting of OmpF, which disrupts bacterial membrane integrity and energy metabolism, providing a promising candidate strategy for combating infections caused by the tested antibiotic-resistant E. coli.