Abstract: In order to investigate the inhibitory effect of catechin and reuterin (3-hydroxypropionaldehyde (3-HPA)) on the caries pathogen Streptococcus mutans and to dissect the underlying mechanisms, the minimum inhibitory concentrations of reuterin and catechin alone and in combination were determined in the present study. By calculating the fractional inhibitory concentration index (FICI), it was found that catechin (1/8 MIC) and 3-HPA (1/4 MIC) had a synergistic effect when used together. The combination of the two drug resulted in a significant reduction in the contents of biofilm, extracellular polysaccharide (EPS) and organic acid (P < 0.05), more effective than either drug alone. Scanning electron microscopic results showed that the biofilm structure in the combination treatment group significantly changed compared to either individual treatment group, accompanied by a decrease in biofilm thickness and the number of bacterial cells. Collectively, the above results demonstrated that the combination treatment of catechin and 3-HPA could inhibit bacterial aggregation and adhesion, impede bacterial cells from being involved in substrate metabolism, increase acidity and delay biofilm?growth?and?maturation, and thus could be used as a novel antibacterial agent against caries. This study will provide a theoretical basis for the development of natural and safe anti-caries products.

Key words: reuterin; catechin; synergistic effect; Streptococcus mutans; biofilm