Isolation and characterisation of antibacterial compounds from <i>Combretum apiculatum</i> subspecies <i>apiculatum</i> (Combretaceae) leaves
Aims: To isolate the antibacterial compounds and to investigate the activity of extracts of, and the antibacterial flavonoids isolated from leaves of Combretum apiculatum against four important community-acquired and nosocomial bacterial pathogens viz. Staphylococcus aureus, Enterococcus faecalis, Escherichia coli and Pseudomonas aeruginosa.
Methods and results: Ten organic and aqueous extracts of the leaf powder of Combretum apiculatum Sond subsp. apiculatum Exell were initially tested against S. aureus, E. faecalis, E. coli and P. aeruginosa using a serial dilution microtitre plate and bioautography assays using p-iodonitrotetrazolium violet (INT) as indicator of growth. The acetone extract was the most potent and selected for further bioassay-guided fractionation of antibacterial compounds which resulted in the isolation of three known flavonoids viz. flavokawain, alpinetin and pinocembrin.
Conclusions: The flavonoids which were isolated from C. apiculatum for the first time were moderately active against S. aureus and E. faecalis with MICs of 40 μg/ml. Ethyl ether and ethyl acetate extracts were equally active against E. faecalis pointing to synergistic effects of phytochemical constituents in exerting antibacterial activity.
Significance and impact of the research: The Combretaceae taxa are important materia medica in Africa and Asia. The results confirm the validity of using C. apiculatum crude extracts against bacterial infections and the superiority of extracts over isolated individual compounds.