Flavonoids from and their synergistic antibacterial effects on drug-resistant .

Abstract

This study seeks to discover flavonoids from a traditional Chinese herb, L., with synergistic antibacterial effects against multidrug-resistant . Five flavonoids, artemetin (), chrysosplenetin (), pachypodol (), penduletin () and chrysoeriol () were obtained by various column chromatographic methods. Their chemical structures were determined on the basis of comprehensive spectroscopic analysis and comparison with literature data. Three of the compounds (, and ) exhibited synergistic activity when combined with norfloxacin against SA1199B, an effluxing fluoroquinolone-resistant strain. The fractional inhibitory concentration indices (FICIs) of and in combination with norfloxacin were 0.375, 0.079 and 0.266 respectively, suggesting synergy. Compound also showed synergistic effects against EMRSA-15 and EMRSA-16 when combined with ciprofloxacin and oxacillin exhibiting FICIs of 0.024 and 0.375 respectively. Real time ethidium bromide (EtBr) efflux assay, qRT-PCR and molecular docking were employed to explore the mechanisms of the synergistic effects.