Inhibition of dextransucrase activity in Streptococcus mutans by plant phenolics

Streptococcus mutans is responsible for causing dental caries in humans and utilizes sucrose for its growth. The dextransucrase (EC 2.4.1.5) is responsible for sucrose metabolism, which exhibits both hydrolytic and glucosyltransferase activities. In this study, we examined the effects of the plant phenols, namely gallic, tannic and syringic acids and aqueous extracts of certain traditionally used chewing sticks (Acacia arabica, Azadirachta indica, Pongamia pinnata and Salvadora persica) for prevention of dental caries on hydrolytic activity of dextransucrsae in S. mutans. Gallic acid (4-5 mM) produced 80-90% inhibition of the enzyme, while tannic acid (0.2 mM) and syringic acid (5 mM) inhibited the enzyme activity 80% and 48%, respectively in vitro. The aqueous extracts of chewing sticks produced 35-40% inhibition of dextransucrase activity at 5 mg phenol concentration. Kinetic analysis revealed mixed-type of enzyme inhibition by polyphenols, where both K(m) and V(max) were altered. The value of K(i) for tannic, gallic and syringic acids were 0.35, 1.6 and 1.94 mM, respectively. The enzyme inhibition by polyphenols was optimum at pH 7-7.5, while by plant extract was maximum at pH 5-6. These results suggest that plant polyphenols may find potential applications in the prevention and control of dental caries by inhibiting dextransucrase activity in S. mutans.