Isolation and characterisation of antibacterial compounds from Combretum apiculatum subspecies apiculatum (Combretaceae) leaves

Abstract

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.DOEL : Om antibakteriese verbindings te isoleer en die aktiwiteit van ekstrakte, fraksies en antibakteriese verbindings uit Combretum apiculatum subsp. apiculatum blare teen vier belangrike bakteriese patogene Staphylococcus aureus, Enterococcus faecalis, Escherichia coli en Pseudomonas aeruginosa te bepaal. METODES EN RESULTATE : Die aktiwiteit van tien organiese en watererige ekstrakte van blare teen Staphylococcus aureus, Enterococcus faecalis, Escherichia coli en Pseudomonas aeruginosa is bepaal deur ’n reeksverdunnings in mikroplate en bio-outografie met p-jodonitrotetrazolium pers (INT) as aanduider van groei. Die asetoonekstrak het die hoogste aktiwiteit gehad en is gebruik om die antibakteriese verbindings te isoleer en te karakteriseer. Drie bekende flavonoiede- flavokawein, alpinetien en pinesembrien was verantwoordelik vir die aktiwiteit. GEVOLGTREKKINGS : Die flavonoiede wat vir die eerste keer uit hierdie spesie geïsoleer is, was redelik aktief teen die twee Gram-positiewe bakterieë Staphylococcus aureus en Enterococcus faecalis met minimum inhiberende konsentrasies (MIK) van 40 μg/ml. Die etieleter en etielasetaat ru-ekstrakte het dieselfde aktiwiteit teen E. faecalis gehad as die geïsoleerde verbindings wat daarop dui dat daar sinergistiese interaksies tussen verbindings in die ekstrak was. IMPAK VAN DIE NAVORSING : Lede van die Combretaceae word wyd in Afrika en Asië gebruik vir medisinale doeleindes. Die navorsing ondersteun die tradisionele gebruik teen infeksies en dui ook daarop dat dit meer voordelig is om ekstrakte te gebruik as die geïsoleerde antibakteriese verbindings.