Isolation and characterization of an antibacterial biflavonoid from an African chewing stick Garcinia kola Heckel (Clusiaceae)

Abstract

Ethnopharmacological relevanceThe use of African chewing sticks in maintaining oral health is widely practiced in African countries. It has been reported that chewing stick users have a lower rate of dental caries and a better general oral health than non-users. It is generally thought that the beneficial effect of chewing stick is attributed to the mechanical cleansing effect and antimicrobial substances present in the stick. However, the active antimicrobial substances remain uncharacterized. Aim of the studyTo provide a scientific basis for the anti-caries effect of African chewing sticks, the authors purify an active antibacterial compound from Garcinia kola Heckel, a Nigerian chewing stick and examined the antibacterial activity of this compound against the cariogenic bacterium Streptococcus mutans. Materials and methodsMethanol extract was prepared from Garcinia kola and was further fractionated by solvent extractions. Silica gel chromatography was used to purify the antibacterial compound from the active fraction. The identity of the purified compound was determined by NMR analysis. The antibacterial activity of the purified compound was examined by standard microbiological assays. ResultsThe antibacterial activity was found in the ether fraction and the active compound was isolated and determined to be a biflavonoid named GB1. GB1 was active against Streptococcus mutans and other oral bacteria with minimum inhibitory concentration (MIC) values of 32–64μg/ml. The basis for the antibacterial effect of GB1 was investigated using Streptococcus mutans as the target. At 256μg/ml, GB1 exhibited some bacteriocidal activity against Streptococcus mutans and induced the aggregation of Streptococcus mutans. GB1 has no apparent effects on protein synthesis and DNA synthesis but inhibited glucose uptake and utilization by Streptococcus mutans suggesting that GB1 exerts its antibacterial effect by inhibiting metabolism. GB1 also inhibited the formation of water-insoluble glucan by the extracellular glucosyltransferases from Streptococcus mutans in a dose-dependent manner. Streptococcus mutans did not develop resistance to GB1 upon subculturing in the presence of sub-MIC level of the biflavonoid. ConclusionThe antibacterial effect and glucan synthesis-inhibition property of this biflavonoid may account for some of the beneficial effects reported in the chewing stick users.