Accessing Citrus and Soybean Flavonoids as Potential Efflux Pump Inhibitors in Drug-Resistant Escherichia coli

Drug efflux pumps represent a significant challenge that contributes to the development of antibiotic resistance in bacteria. This research aimed to evaluate the flavonoids apigenin, chrysin, glycitein, and hesperetin for their potential to inhibit efflux pumps in drug-resistant Escherichia coli.

The antibacterial activity of the flavonoids was assessed using minimum inhibitory concentration (MIC) and modulation assays. Dye accumulation and efflux assays were performed to evaluate effects on efflux pump function, while membrane permeability and biofilm formation assays were also conducted. Molecular docking was used to examine interactions between the flavonoids and the AcrB efflux transporter.

Although the flavonoids showed limited intrinsic antibacterial activity, they enhanced the effectiveness of erythromycin, ciprofloxacin, and clarithromycin against drug-resistant E. coli. Apigenin and hesperetin significantly increased dye accumulation and reduced dye efflux, indicating interference with substrate translocation through efflux pumps. All compounds exhibited no effect on inner membrane permeability, while apigenin, chrysin, and glycitein inhibited biofilm formation. Docking results showed that apigenin and chrysin bind favorably within the distal binding pocket of AcrB, forming hydrophobic and π-π interactions with key aromatic residues such as Phe610 and Phe628, with binding affinities of -8.8 to -8.9 kcal/mol.

The results suggest that apigenin and chrysin have promising efflux-pump inhibitory potential in drug-resistant E. coli, supporting their possible role as adjuvants to improve antibiotic efficacy.