Inhibitory Effects of Fruit Berry Extracts on Streptococcus mutans Biofilms

Objectives: There is interest in using natural products to inhibit virulence properties of cariogenic bacteria. High-coloured fruit berries are among the best dietary sources of phytochemicals and further research into its effects on oral diseases is warranted. This study investigated the effects of polyphenol-rich functional extracts of cranberry, wild blueberry, and strawberry on Streptococcus mutans biofilms.
Methods: High-quality organic extracts of cranberry, wild blueberry, strawberry and a combination of the 3 berry extracts (Orophenol) were used to treat 24 hour-old S. mutans biofilms grown on hydroxyapatite discs, using the Amsterdam Active Attachment biofilm model. Biofilms were treated for 1 hour using concentrations from 62.5 to 500µg/ml, and different assays carried out to evaluate the effects of the berry extracts on biofilm properties. Biofilm metabolism was assessed using the XTT reduction assay. Biofilm volume and structural organisation were assessed by confocal laser scanning microscopic imaging after in situ labelling of the biofilm components. Microbial viability was assessed by CFU counts.
Results: The highest reduction in metabolic activity (29-32%) was seen when the S. mutans biofilms were treated with 250-500µg/ml of cranberry extract (P<0.001). Blueberry extracts suppressed metabolic activity only at 500µg/ml (10% reduction, P=0.041), while strawberry extracts had no effects on biofilm metabolism. Orophenol reduced metabolic activity at 500µg/ml (25%, P<0.001), 250µg/ml (22%, P<0.001), and 125µg/ml (18%, P=0.002). Biofilms treated with test agents showed slightly lower numbers of recoverable viable cells compared with the vehicle control, however none were bactericidal for S. mutans in the biofilms. The biovolumes of exopolysaccharides and bacterial cells in biofilms treated with 500µg/ml of cranberry extract and Orophenol were significantly lower those of biofilms treated with vehicle control (P=0.028), showing effects on biofilm structural architecture.
Conclusions: Cranberry showed the best potential to disrupt S. mutans biofilms without significantly affecting bacterial viability.