The Antimicrobial Properties of Epigallocatechin Gallate on Streptococcus mutans

Objectives: The prevention of dental caries by the antimicrobial property of green tea-derived epigallocatechin gallate (EGCG) has been considered. However, the detailed antimicrobial mechanism of EGCG is still controversial. Thus, we intended to investigate the underlying mechanism through examining the bactericidal activity of EGCG on Streptococcus mutans and its effect on acid production and aggregation of S. mutans.
Methods: S. mutans NCTC10449 was used in this study. To test the bactericidal activity of EGCG, bacterial colonies were counted after the exposure of bacteria to different concentrations of EGCG. The pH-stat system was used to evaluate bacterial acid production from glucose under anaerobic condition in the presence and absence of EGCG. The aggregation of planktonic bacteria caused by EGCG was evaluated by optical density at 660 nm. To test the influence of saliva, stimulated saliva was collected from five volunteers and applied to the above experiments.
Results: 2 mg/ml EGCG showed no bactericidal activity on S. mutans after 5 hours co-incubation, while 1 mg/ml EGCG decreased acid production by S. mutans both at pH 7.0 and pH 5.5. 2 mg/ml EGCG caused bacterial cell aggregation and reduced the optical density of cell suspension by 80%. In the presence of saliva, EGCG also repressed the pH fall and caused bacterial aggregation in the bacterial suspension.
Conclusions: EGCG can inhibit the acid production of S. mutans. EGCG also can promote bacterial aggregation, suggesting its potential to inhibit bacterial adhesion to the tooth surface and the subsequent biofilm formation. Moreover, stimulated saliva did not influence these properties of EGCG on the acid production and the aggregation of S. mutans. These results indicate that green tea-derived EGCG has the potential to prevent dental caries.