Abstract
Green tea-derived catechins, which can be divided into galloylated (epicatechin gallate: ECG, epigallocatechin gallate: EGCG) and non-galloylated (catechin: C, epicatechin: EC, epigallocatechin: EGC) catechins, are considered to be the main contributors to the caries control potential of green tea. In this study, we intended to compare the antimicrobial effects of these representative green tea-derived catechins and their combined effects with fluoride on the acid production and aggregation of Streptococcus mutans. The effects of different catechins on the growth, aggregation and acid production of S. mutans, and the combined effect of catechins and potassium fluoride (2 mm at pH 7.0, 0.3 mm at pH 5.5) on S. mutans acid production were measured by anaerobic culture, turbidity changes due to aggregation, and pH-stat methods. Molecular docking simulations were also performed to investigate the interactions between catechins and membrane-embedded enzyme II complex (EIIC), a component of the phosphoenolpyruvate-dependent phosphotransferase system (sugar uptake-related enzyme). ECG or EGCG at 1 mg/mL significantly inhibited the growth of S. mutans, induced bacterial aggregation, and decreased glucose-induced acid production (p < 0.05). All catechins were able to bind to EIIC in silico, in the following order of affinity: EGCG, ECG, EGC, EC, and C. Furthermore, they enhanced the inhibitory effects of fluoride at pH 5.5 and significantly inhibited S. mutans acid production by 47.5-86.6% (p < 0.05). These results suggest that both galloylated and non-galloylated catechins exhibit antimicrobial activity, although the former type demonstrates stronger activity, and that the caries control effects of green tea may be due to the combined effects of multiple components, such as catechins and fluoride. The detailed mechanisms underlying these phenomena and the in vivo effect need to be explored further.