The aim of this study was to evaluate synergy and inhibitory effects of xylitol and erythritol on Streptococcus mutans and Streptococcus sobrinus growth and biomass production on a polystyrene plastic surface. Study design; S. mutans and sobrinus strains (American Type Culture Collection reference strains 31341, 35668, 25175, sobrinus 33478) were cultivated in media (Todd Hewitt Broth with 1% sucrose or heart-brain infusion broth with 1% sucrose) at differing concentrations of xylitol or erythritol in microtiter assay plates incubated for 48 hours. Bacterial growth was quantified and measured by optical density using a microplate reader. Experiments assessing synergy and biofilm growth were carried out also using microdilution assays. All four strains were inhibited by 30% (w/v) xylitol, and 15% erythritol at 150mg/ml erythritol, 2/4 strains had reduced growth; at 270mg/ml, 4/4 strains were inhibited. Bactericidal effects were not observed at any polyol concentration. Combinations of both polyols in a checker board array were used to determine if there were any benefits of polyol combinations. Results The combination studies yielded mixed outcomes with indifference in growth for strains 68 and 78, potential additive effect for strain 75 and possible antagonism for strain 41. Assessment of biomass formation and polyol interference were also performed post MIC assessment. Strains 41, 68 and 75 produced significant biomass in the absence of either polyol. Both polyols inhibited biomass formation in a dose-dependent fashion. Strain 75 is a poor biomass producer and could not be assessed for polyol effects in our assay. Conclusion: Our results demonstrate significant polyol influence on the oral Streptococcal strains tested in our laboratory.

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