Effect of erythritol on Streptococcus mutans growth and biofilm

Sugar alcohols such as xylitol have been used as sucrose substitutes for the reduction of dental caries.  We hypothesize that erythritol, a four-carbon sugar alcohol, exhibits similar inhibitory properties as xylitol against Streptococcus mutans growth and biofilm.  Objective: To determine the in vitro effect of erythritol on growth, acid production, metabolic activity and biofilm formation of S. mutans. Xylitol was used for comparison.  Methods: S. mutans UA159 was used in this study.  The effect of erythritol on growth and biofilm formation of S. mutans was examined in a chemically defined medium (CDM) supplemented with glucose as the carbon source.  Assays to determine growth, metabolic activity (XTT) and biofilm formation were performed in 96-well microtiter plates containing erythritol (0.15%-15% or 12.5-1200mM) at 37C for 48hr anaerobically.  Results: As sole carbon source, erythritol at ≥ 0.1% did not support growth of S. mutans.  Growth inhibition was observed when media glucose concentration was between 0.5-2%. The minimum inhibitory concentrations of erythritol in CDM (1% glucose) was >10%. Higher MIC values for erythritol were noted in CDM with 4% glucose.  Dose dependent inhibition was observed when S. mutans was grown in BHI (0.5X) supplemented with erythritol (50 mM-1200 mM) over a 24 hr period, although less effective than xylitol.  Compared to the non-treated controls, S. mutans biofilm formed in the presence of erythritol was less adherent and easily removed upon rinsing. Erythritol did not promote further growth of preformed biofilm. However, the metabolic activity of xylitol or erythritol grown biofilms were not significantly inhibited. Conclusions: Based on the experimental conditions employed in this study, erythritol affected the S. mutans biofilm formation but was a less effective growth inhibitor compared to xylitol.  Growth media and the availability of glucose play an important role when assessing the effect of sugar alcohols on S. mutans virulence factors.