Inhibitory effects of green tea polyphenol epigallocatechin gallate (EGCG) on exopolysaccharide production by Streptococcus mutans under microfluidic conditions

Plaque-forming microorganisms produce insoluble exopolysaccharide (EPS), which allows the microorganisms to attach strongly to the tooth surface. Then, they start forming biofilm, which is responsible for plaque formation. The green tea polyphenol epigallocatechin gallate (EGCG) is known to inhibit biofilm formation of oral bacteria. However, its inhibitory effects on biofilm formation between the teeth have not been well studied due to the lack of devices that mimic the space between the teeth. In this study, we used a microfluidic device packed with glass beads (250–300 µm in diameter) to mimic the small cavities between the teeth in order to test the inhibitory effects of EGCG on the biofilm formation of Streptococcus mutans, one of the plaque-forming microorganisms. EPS production by S. mutans was more effectively inhibited by EGCG in the microfluidic device, compared to on agar plates, suggesting that it is more effective against biofilm formation by S. mutans cells under flow conditions than under non-flow conditions, such as conditions achieved by agar plates. These results suggest that our microfluidic device may be highly useful for studying the actual effects of antimicrobial compounds against plaqueforming microorganisms.