Sanggenon D from root bark of mulberry inhibits the growth of Staphylococcus aureus by moderating the fatty acid biosynthesis system

Mulberry trees are an important crop widely cultivated in the Americas, Eurasia and Africa. Various prenylated flavonoids with different bioactivities have been identified in mulberry root bark. The objective of this study was to investigate antibacterial properties of several prenylated flavonoids from mulberry root bark and elucidate their mechanism(s) of action toward bacteria. Minimum inhibitory concentrations and time-dependent inhibiting curves of bacteria treated with mulberry root bark prenylated flavonoids were applied to identify bacteriostatic effects. Antibacterial effects were observed toward Staphylococcus aureus and Escherichia coli, the strongest effect was of sanggenon D toward Staphylococcus aureus. Scanning electron microscopy was used to observe structural changes of Staphylococcus aureus cells, gas chromatography-mass spectrometry was used to investigate the fatty acid components in cells, and assessment by quantitative real-time PCR was applied to elucidate changes in expression of fatty acid biosynthesis enzyme system-associated genes on sanggenon D treatment. The mechanism of the anti- Staphylococcus aureus activity of sanggenon D involves downregulation of expression of fatty acid biosynthesis enzyme-encoding genes, which may in turn affect biosynthesis of the Staphylococcus aureus cell membrane. Collectively, our results reveal that sanggenon D from mulberry root bark shows a potent antibacterial effect.