Abstract:

Objective

To study the effect of inactivation htrA or clpP on the the acid tolerance of Streptococcus mutans.

Methods

Strains were grown to mid-logarithmic growth phase and devided into experimental group and control group. Experimental group was resuspended in TPY with pH 5.5 for 5 h as adapted strains. The control group was treated in TPY at pH 7.0 for 5 h as unadapted strains. Then the two groups were sustained in a lethal TPY with pH 3.0 for 3 h，the survival rate of strain was calculated every hour. All the data were statistically analyzed.

Results

The survival rates of the three unadapted strains was not statistically significant within 3 h（P ＞0.05）. The viabilities of the survival rate of htrA adapted mutant strain and clpP adapted mutant strain was significantly lower than that of adapted standard stain （P ＜0.05）. Compared with the survival rate of htrA adapted mutant strain， there were no obvious differences in the survival rate of the clpP adapted mutant strain （P ＞0.05）. The survival rates of adapted standard strain and htrA adapted mutant strain were higher than that of the same unadapted strains （P ＜0.05）. The effect of TPY at pH 5.5 on strain was higher than that of the two genes knockouted （P ＜0.05）.

Conclusions

Compared with Streptococcus mutans standard strain， the abilities of the acid tolerance of htrA mutant strain and clpP mutant strain declined to various degrees.

Key words: Streptococcus mutans, htrA gene, clpP gene, Acid tolerance