Abstract: Objective To investigate the effects of a combination of aloin and chlorogenic acid on the growth, acid production, adhesion and biofilm formation of Streptococcus mutans(SM). 
Methods The minimum inhibitory concentration(MIC)  of aloin and chlorogenic acid against S.mutans were determined by liquid double micro-dilution method. MIC of mixed solution of aloin and chlorogenic acid against S.mutans was determined by the checkerboard dilution method. Fractional inhibitory concentration(FIC) index was used to evaluate the combined inhibitory effect of aloin and chlorogenic acid against S.mutans. The effect of mixed solution of aloin and chlorogenic acid, with 5 concentration gradients concentrations lower than MIC on the acid production of S.mutans, was also observed. The 24 h biofilm model of S.mutans was constructed in vitro, and MTT method was used to determine the amounts of biofilm adhesion after the above-mentioned mixture were applied for 24 h. The effects on biofilm structure and bacterial activities were observed by confocal laser scanning microscope(CLSM). 
Results When aloin and chlorogenic acid were used alone, the MIC was 0.63 g/L and 5 g/L respectively, respectively. Aloin 0.31 g/L combined with chlorogenic acid 2.5 g/L could reach MIC, with an FIC of 1. As the concentration of the mixture increased, the △pH and OD values of S.mutans was decreased(P＜0.05). CLSM showed that the structure of S.mutans biofilm became thinner and the number of live bacteria decreased with the increase of the concentrations of the mixed solution.   
Conclusion The combination of aloin and chlorogenic acid has an additive effect on the in vitro antibacterial activity of S.mutans, which can effectively inhibit the growth, acid production and adhesion of S.mutans at a lower concentration than the single component.

Key words: streptococcus mutans, aloin, chlorogenic acid