Green Tea Electrostatic Inhibition of S. mutans Binding to Hydroxyapatite

Green tea inhibits the binding of bacteria to enamel. We think electrical interactions may be involved making the zeta potential, ζ, a relevant electrical property to measure. We have investigated the effects of oolong tea extract (OTE) on ζ for SM (S. mutans), HA (hydroxyapatite) and saliva-coated HA (salHA) and on the binding of SM to HA and to salHA. Objective: To correlate changes in SM binding to HA and salHA with OTE-induced changes in ζ for each species. Methods: SM, HA (20 μm diameter beads), and salHA are incubated independently with OTE and then washed. Electrophoretic mobilities, μ_e, are measured by phase analysis light scattering, and values of ζ are calculated from μ_e using the Smoluchowski equation. Relative binding strengths are determined by measuring the free [SM] after removing the bound by sedimentation. Results: OTE increases the magnitude of -ζ for SM, and salHA and decreases the magnitude of -ζ for HA. The product of ζ_BEAD x ζ_BACTERIA has a linear negative inverse correlation with binding, with different slopes for HA and salHA. Conclusions: Increased non-specific electrostatic repulsion from increased -ζ is a major mechanism by which green tea inhibits SM binding. The different slopes and intercepts for the ζ_BEAD x ζ_BACTERIA dependences of binding are likely due to specific electrical and non-electrical contributions to binding in the absence and presence of saliva.