目的

探讨htrA、clpP 基因缺失对变异链球菌耐酸性的影响。

方法

变异链球菌标准株及htrA 缺陷株、clpP 缺陷株培养至对数中期分成两组，一组作为实验组进行5 h 预酸化处理（pH=5.5），一组作为对照组在普通乳酪消化胨酵母（TPY）培养液中处理5 h，然后将两组菌株在致死性酸环境（pH=3.0）处理3 h，每隔1 h 取菌液采用平板活菌计数法测定活菌数，计算得到生存率，统计学分析。

结果

3 h 内，未经预酸化处理三种菌株生存率相比差异无统计学意义（P ＞0.05），预酸化处理后，与标准株相比htrA 缺陷株和clpP 缺陷株生存率都有下降（P ＜0.05），两种缺陷株相比生存率差异无统计学意义（P ＞0.05），预酸化处理的标准株和htrA 缺陷株生存率均明显高于未经预酸化处理（P ＜0.05），预酸化处理对生存率的影响大于两种基因分别缺失（P ＜0.05）。

结论

与变异链球菌标准株相比，htrA 缺陷株和clpP 缺陷株耐酸能力有不同程度的下降。

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.