Synergistic Effects and Mechanisms of Action of Rutin with Conventional Antibiotics Against Escherichia coli

Rutin is a widely known plant secondary metabolite that exhibits multiple physiological functions. The present study focused on screening for synergistic antibacterial combinations containing rutin, and further explored the mechanisms behind this synergy. In vitro antibacterial test results of rutin showed that the ranges of minimum inhibitory concentration (MIC) and Minimum bactericidal concentration (MBC) are 0.125-1 and 0.125-2 mg/mL, respectively. However, rutin and amikacin have a significant synergistic effect, with a fractional inhibitory concentration index (FICI) range of 0.1875-0.5. The time bactericidal curve proved that the combination of rutin and amikacin inhibited bacterial growth within 8 h. Scanning electron microscopy (SEM) revealed that a low-dose combination treatment could disrupt the cell membrane of <i>Escherichia coli</i> (<i>E. coli</i>). A comprehensive analysis using alkaline phosphatase (AKP), K⁺, and a protein leakage assay revealed that co-treatment destroyed the cell membrane of <i>E. coli</i>, resulting in the significant leakage of AKP, intracellular K⁺, and proteins. Moreover, confocal laser scanning microscopy (CLSM) and red-green cell ratio analysis indicated severe damage to the <i>E. coli</i> cell membrane following the co-treatment of rutin and amikacin. This study indicates the remarkable potential of strategically selecting antibacterial agents with maximum synergistic effect, which could significantly control antibiotic resistance.