Inhibitory effect of xylitol and stevia extract on Streptococcus sobrinus

Stevia extract, commercially available as a white powder, contains stevioside and rebaudioside A, two natural sweeteners, which are accepted for use as sweeteners and are claimed to have anti-caries activity. Objective: The objective of this study was to compare the effects of commercially available xylitol and stevia extract on caries-inducing properties of Streptococcus sobrinus. Methods: Growth rate was determined by measuring optical density of S. sobrinus 6715 culture, acid production by pH measurement, extracellular polysaccharide production by alkali precipitation and carbohydrate determination using Nelson Somogyi assay, cell surface hydrophobicity by solubility in hexadecane, cellular aggregation by turbidity determination and adhesion properties of S. sorbrinus 6715 on a saliva coated plate by staining attached cells with crystal violet. The effects of xylitol and stevia extract on these properties were tested. Results: Both stevia extract and xylitol (20% w/v) showed similar inhibitory effect on growth rate (50% inhibition) and reduced the rate of acid production of S. sobrinus. Stevia extract (20% w/v) significantly decreased cell surface hydrophobicity, induced cellular aggregation and inhibited extracellular polysaccharide production when compared to xylitol (20% w/v). Furthermore, the adherence of bacteria to saliva-coated plate was inhibited. Conclusions: These results suggested that stevia extract had inhibitory effect on the caries inducing properties of S. sobrinus and could be useful for caries prevention.