Antimicrobial actions of α-mangostin against oral streptococci

The increasing prevalence of dental caries is making it more of a major world health problem. Caries is the direct result of acid production by cariogenic oral bacteria, especially Streptococcus mutans. New and better antimicrobial agents active against cariogenic bacteria are badly needed, especially natural agents derived directly from plants. We have evaluated the inhibitory actions of alpha-mangostin, a xanthone purified from ethanolic extracts of the tropical plant Garcinia mangostana L., by repeated silica gel chromatography. alpha-Mangostin was found to be a potent inhibitor of acid production by S. mutans UA159, active against membrane enzymes, including the F( H+)-ATPase and the phosphoenolpyruvate - sugar phosphotransferase system. alpha-Mangostin also inhibited the glycolytic enzymes aldolase, glyceraldehyde-3-phosphate dehydrogenase, and lactic dehydrogenase. Glycolysis by intact cells in suspensions or biofilms was inhibited by alpha-mangostin at concentrations of 12 and 120 mu mol.L-1, respectively, in a pH-dependent manner, with greater potency at lower pH values. Other targets for inhibition by alpha-mangostin included (i) malolactic fermentation, involved in alkali production from malate, and (ii) NADH oxidase, the major respiratory enzyme for S. mutans. The overall conclusion is that alpha-mangostin is a multitarget inhibitor of mutans streptococci and may be useful as an anticaries agent.