Chemical composition, antimicrobial and anti-quorum sensing activities of pummelo peel flavonoid extract

Many naturally occurring flavonoids detected in plants and spices possess antimicrobial and antioxidant activities and may serve as sources of antimicrobial agents and drugs. Previous studies have shown that virulence expression of pathogenic bacteria relies on quorum sensing (QS) circuits as central regulators. The aim of this study was to characterize the chemical composition of flavonoid extract from pummelo peel (Citrus maxima (Burm.) Merr. cv. Shatian Yu) and to determine its antimicrobial and anti-quorum sensing activities against the selected pathogens, Vibrio anguillarum, and the biosensor strain, Chromobacterium violaceum CV026. The crude flavonoid content of pummelo peel was 5.03 g rutin equivalents (REs)/100 g, and its primary constituents were identified as naringin and acetyl naringin, accounting for 91.62% and 4.37%, respectively. The minimal inhibitory concentration (MIC) of pummelo peel flavonoid extract (PPFE) against the tested bacteria ranged from 0.5 to 4.5 mg REs/mL. At sub-MIC concentrations, pummelo peel flavonoid extract inhibited most of the phenotypes regulated by QS in bacteria. Violacein production in C. violaceum CV026 was inhibited by 73.69% following the addition of 0.9 mg REs/mL PPFE. Moreover, 1.8 mg REs/mL PPFE inhibited biofilm production by 47.93% and 83.54% of the swimming motility in V. anguillarum. Molecular docking analysis of the active components attributes the QS inhibitory activity of PPFE to naringin. These findings suggest that pummelo peel can be used to produce antibacterial agents and as a quorum sensing inhibitor to overcome antimicrobial resistance and side effects.