It has been suggested that green tea-derived epigallocatechin gallate (EGCG), which has antimicrobial properties, might help prevent dental caries. However, the detailed properties of EGCG remain unclear. In this study, the antimicrobial properties of EGCG were evaluated by examining its bactericidal activity, its inhibitory effects against bacterial growth, acid production, acidic end-product formation, and sugar uptake (phosphoenolpyruvate-dependent phosphotransferase system, PEP-PTS activity), and its effects on bacterial aggregation, using monocultured planktonic cells of Streptococcus mutans and non-mutans streptococci. Coincubating S. mutans with EGCG (1 mg/mL) for 4 h had no bactericidal effects, while it decreased the growth and acid production of S. mutans by inhibiting the activity of the PEP-PTS. EGCG (2 mg/mL) caused rapid bacterial cell aggregation and had reduced the optical density of S. mutans cell suspension by 86.7% at pH 7.0 and 90.7% at pH 5.5 after 2 h. 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, these antimicrobial effects of short-term EGCG treatment persisted in the presence of saliva. These results suggest that EGCG might have short-term antibacterial effects on caries-associated streptococci in the oral cavity.
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