Antimicrobial activity of green tea-derived epigallocatechin gallate on Streptococcus mutans and non-mutans streptococci and the characteristic mechanisms

概要

[Introduction] Drinking tea is associated with lower caries levels in humans. Green tea is known to be a rich source of polyphenols including epigallocatechin gallate (EGCG), whose multiple antibacterial activities have been considered in the prevention of dental caries. However, further investigations are still required to illustrate the detailed properties of EGCG. The aim of this study is to characterize the antimicrobial effects of EGCG on caries-associated streptococci.

[Materials and Methods] The antimicrobial properties of EGCG were evaluated by examining its bactericidal activity. The effects of EGCG on bacterial growth, acid production, acidic end-product formation, sugar uptake (phosphoenolpyruvate-dependent phosphotransferase system, PEP-PTS activity), and aggregation of streptococci were also evaluated. To explore the influence of saliva, I further examined the antimicrobial properties of EGCG within stimulated saliva by generating experiments mentioned above.

[Results and Discussion] No bactericidal effects were detected after coincubation of S. mutans with EGCG (1 mg/ml) for 4 hours while it decreased the growth and acid production of S. mutans by inhibiting the activity of the PEP-PTS. 2-hour incubation with EGCG (2 mg/ml) caused rapid aggregation of bacterial cells and reduced the optical density of S. mutans cell suspension by 86.7% at pH 7.0 and 90.7% at pH 5.5. EGCG also reduced the acid production of non-mutans streptococci, including S. sanguinis, S. gordonii, and S. salivarius, and promoted the aggregation of these non-mutans streptococci. Furthermore, short-term EGCG treatment still effectively functioned in the presence of saliva. These results suggest that the short-term antibacterial effects of EGCG might contribute to the caries-preventing properties of green tea, and the daily consumption of green tea might help maintain a healthy oral environment.