Objective To investigate the antibacterial activity of glycyrrhizic acid（GA） against Streptococcus mutans （S. mutans） under acidic environment in vitro. Methods Working culture were prepared by inoculation of S. mutans into TPY broth followed by static incubation under anaerobic condition at 37 ℃ for 24 h. TPY broth was supplemented with three kinds density of GA（0.78, 1.57, 3.13 mg·mL-1）, whose acidity was regulated to pH 7.0, pH 5.5 and pH 4.0. And the group of pH 7.0 was used as negative control. The growth of S. mutans was measured by A600 of bacteria suspension and counting colony forming unit（CFU）. In addition, the survival rate of S. mutans was calculated. Results In pH 5.5 groups, the survival rates of 0.78, 1.57 and 3.13 mg·mL-1 GA groups were 60.96%, 60.27% and 45.58%, respectively, and in pH 4.0 groups, the survival rates were 68.75%, 53.12% and 45.83%. In 0.78, 1.57 and 3.13 mg·mL-1 GA groups, the survival rates of pH 5.5 and pH 4.0 were 52.25% and 39.05%, 74.39% and 43.11%, 86.38% and 55.30%, respectively. Conclusion GA could inhibit the gro wth of S.mutans under acidic environment, which the effect is improved as the acidity increased.
