Antibacterial activity of flavonoids from the stem bark of Erythrina caffra thunb.

The antibacterial activity of the stem bark of Erythrina caffra Thunb. was investigated against different bacterial strains. The antibacterial activity was determined by a micro broth dilution assay. Antibacterial compounds were isolated and identified using a Bruker Avance III LPO NMR spectrometer. Four known flavonoids, abyssione-V 4'-O-methyl ether, 6,8-diprenylgenistein, alpinumisoflavone and burttinone, were isolated. All the compounds were active against both Gram-negative and Gram-positive bacteria. The minimum inhibitory concentration values obtained (MIC) ranged from 3.9 μg/mL to 125 μg/mL. This is the first report of antibacterial activity of burttinone and the isolation of these compounds from E. caffra.