OBJECTIVETo investigate the antibacterial activity of glycyrrhizic acid (GA) against Streptococcus mutans (S. mutans) under acidic environment in vitro.

METHODSWorking culture were prepared by inoculation of S. mutans into TPY broth followed by static incubation under anaerobic condition at 37 degrees C for 24 h. TPY broth was supplemented with three kinds density of GA (0.78, 1.57, 3.13 mg x mL(-1)), whose acidity was regulated to pH7.0, pH 5.5 and pH4.0. 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.

RESULTSIn pH 5.5 groups, the survival rates of 0.78, 1.57 and 3.13 mg x mL(-1) GA groups were 60.96%, 60.27% and 45.58%, respectively, and in pH4.0 groups, the survival rates were 68.75%, 53.12% and 45.83%. In 0.78, 1.57 and 3.13 mg x mL(-1) GA groups, the survival rates of pH5.5 and pH4.0 were 52.25% and 39.05%, 74.39% and 43.11%, 86.38% and 55.30%, respectively.

CONCLUSIONGA could inhibit the growth of S. mutans under acidic environment, which the effect is improved as the acidity increased.