Objectives: The aim of this research was to determine the pH-dependent changes in F-ATPase activity and proton fluxes in Streptococcus mutans (S. mutans) as induced by varying the concentration of fluoride ±10 mM (0.058% (v/v)) ethanol.Methods: S. mutans UA159 was grown in Brain Heart Infusion medium at pH 4.8, 6.8, or 8.8. The FATPase assay was initiated by the addition of ATP, and stopped by adding 10% trichloroacetic acid. For the proton flux assay, bacterial suspensions were titrated to pH 4.6 with 0.5 M HCl, and then 0.5 M HCl was added to decrease the pH values in units of approximately 0.4 pH. The subsequent increase in pH was monitored using a glass electrode. To disrupt the cell membrane, 10% (v/v) butanol was added to the suspensions after 80 minutes.Results: At all pH levels, fluoride ±10 mM ethanol not only decreased F-ATPase activity but also increased the proton permeability of S. mutans. The largest effects were observed at pH 4.8. Ethanol enhanced these effects only at pH 4.8.Conclusions: A very low concentration of ethanol enhanced the action of fluoride on F-ATPase activity and the proton permeability in S. mutans at acidic pH levels. We expect that low concentrations of ethanol may be used together with fluoride and/or other anticaries agents to develop more effective anticaries preparations.

Keywords: ethanol, F-ATPase, Fluoride, pH stress, proton permeability, Streptococcus mutans