Antibacterial Activity of Stilbenes Isolated From Reynoutria japonica Against Vancomycin-resistant Enterococci: An In Vitro and In Silico Approach

Abstract

Enterococcus species are Gram-positive cocci normally found in the gut but have emerged as opportunistic pathogens in healthcare settings, with rising multidrug resistance, particularly vancomycin-resistant Enterococci (VRE) posing major therapeutic challenges. This study evaluated the antibacterial and synergistic effects of plant-derived stilbenes from Reynoutria japonica against clinical VRE isolates. Ten clinical Enterococcus faecalis isolates were identified using standard morphological, biochemical, and Gram-staining methods, and antibiotic susceptibility testing. The antibacterial activity of polydatin, resveratroloside, and trans-resveratrol was assessed by agar well diffusion, and evaluation of minimum inhibitory concentrations (MICs) and evaluation of bactericidal activity concentrations (MBCs), with synergistic effects tested in combination with vancomycin. Molecular docking was performed with DapF, vanA, and gelE proteins. All isolates were resistant to vancomycin, ampicillin, imipenem, gentamicin, and ciprofloxacin but sensitive to linezolid. All three stilbenes displayed antibacterial activity. Notably, trans-resveratrol was the most active compound, with a MIC value of 0.156 mM and bactericidal activity (an MBC value equal to the MIC). Furthermore, all compounds exhibited synergistic effects when combined with vancomycin. Phytochemical analysis confirmed these stilbenes as major constituents in the root extract of R. japonica. Molecular docking studies revealed strong binding affinities of the compounds to key virulence and resistance-associated proteins (DapF, VanA, and GelE). These results indicate that trans-resveratrol and related stilbenes are promising candidates for development as alternative or adjunct therapeutic agents against VRE infections. Additionally, this study substantiates the traditional use of R. japonica as a source of bioactive antimicrobial compounds.