Effect of glucose concentrations on acidogenicity of Streptococcus mutans

Objectives: To evaluate the effect of the amount of glucose in the broth on the acidogenicity of the Streptococcus mutans isolates. Methods: Twenty-eight strains of Streptococcus mutans (serotype C) were used, acquired from the previous study. Twelve of them were isolated from caries-free persons, and sixteen from caries-active patients. The strains were inoculated in TPY broth containing glucose with the concentration of 0.2%,0.5%, 1%, 2% or 5%(g/100ml) respectively, and grew for 24 hours under anaerobic conditions at 37°C. The pH values before inoculation and the terminal pH values were measured with pH elecotrode, and the dpH values were determined as the acidogenic abilities of the strains. The acidogenicity difference among strains cultured in broth with different glucose concentrations was evaluated by ANOVA, and q test was used to evaluate the difference between each two concentrations. The acidogenicity differences between strains from caries-free and caries-active persons were compared by t test. Results: The acidogenic abilities of the strains were significantly different under different glucose concentrations, and the strains cultured with 0.2% glucose produced less acid than others (p<0.01). The difference of acidogenic abilities between strains from caries-free and caries-active persons was not significant (p>0.05). Conclusion: The acidogenic abilities of Streptococcus mutans were repressed under starved conditions, while excessive amount of glucose had no significant effect on those.It is to be determined whether the acidogenic gene expression chages when bacteria are cultured with different glucose concentrations.