Antibacterial property of isoflavonoids isolated from Erythrina variegata against cariogenic oral bacteria.

The antibacterial property of 7 compounds, isolated from Erythrina variegata (Leguminosae) by repeated silica gel column chromatography, against cariogenic oral bacteria was investigated. Extensive spectroscopic study revealed that all were isoflavonoids. Among them, 3,9-dihydroxy-2,10-di(gamma,gamma-dimethylallyl)-6a,11a-dehydropterocarpan (erycristagallin) showed the highest antibacterial activity against mutans streptococci, other oral streptococci, Actinomyces and Lactobacillus species with a minimum inhibitory concentration (MIC) range of 1.56-6.25 microg/ml, followed by 3,6a-dihydroxy-9-methoxy-2,10-di(gamma,gamma-dimethylallyl)pterocarpan (erystagallinA) and 9-hydroxy-3-methoxy-2-gamma,gamma-dimethylallylpterocarpan (orientanol B) (MIC range: 3.13-12.5 microg/ml). The antibacterial effect of erycristagallin to mutans streptococci was based on a bactericidal action. Erycristagallin (6.25 microg/ml: MIC) completely inhibited incorporation of radio-labelled thymidine into Streptococcus mutans cells. Incorporation of radio-labelled glucose into bacterial cells was also strongly inhibited at MIC, and 1/2 MIC of the compound reduced the incorporation approximately by half. The findings indicate that erycristagallin has a potential as potent phytochemical agent for prevention of dental caries by inhibiting the growth of cariogenic bacteria and by interfering with incorporation of glucose responsible for production of organic acids.