中文摘要：

已知右旋氨基酸参与了细菌细胞壁肽聚糖的形成，但尚未有实验对其如何影响致龋茵变异链球茵进行研究。本实验成功构建了变异链球菌丙氨酸消旋酶alr缺失型突变茵IFD140△alr。表型观察突变株茵落外观和生长情况与野生株无明显差异，但生长曲线提示对数生长期之后比野生株生长快，且饱和浓度较高。扫描电镜显示突变株相较野生株形成了更厚更致密的生物膜。通过变异链球菌alr缺失突变菌株的构建成功，提示右旋氨基酸可能对维持变异链球菌的正常生长和形成生物膜有重要作用。

英文摘要：

It is known that D-amino acids （D-aa） involve in the formation of bacterial cell wall peptidoglycan, but there have been no reports about how D-aa affects the cariogenic Streptococcus mutans. A ,S. mutans alr （ alanine racemase） deletion mutant IFD140△alr was successfully constructed. There was no significant difference between the mutant strains and wild strain on their phenotype of colony morphology and their growth, however, the growth curve showed that after logarithmic phase the mutant strain grew faster than wild strain, and in addition the saturated concentration was fairly high. Scanning electron microscopy showed that thicker and denser biofilms were formed by alr mu- tant strain as compared with wild-type. The successful construction of alr deletion S. mutans indicated that D-aa may have an important role on the maintenance of normal growth and biofilm formation of S. mutans.