State Key Laboratory of Oral Diseases, West China Hospital of Stomatology, Sichuan University, NO. 14, 3rd Section of South RenMin Rd, Chengdu, Sichuan, 610041, China.
Department of Operative Dentistry and Endodontics, West China Hospital of Stomatology, Sichuan University, Chengdu, Sichuan, China.
Sci Rep. 2018 Apr 13;8(1):5984. doi: 10.1038/s41598-018-24295-1.
The enzyme alanine racemase (Alr) has been a new target for the development of antibacterial drugs based on the involvement of D-Ala in bacterial cell wall biosynthesis. Our previous study noted that Alr is essential for the growth and interspecies competitiveness of S. mutans, the major causative organism of dental caries. However, physiological activity and cariogenicity of S. mutans affected by Alr remains unknown. The current study examined the biofilm biomass, biofilm structure, extracellular polysaccharide (EPS) synthesis, glucosyltransferase (gtf) gene expression, acid production and acid tolerance in the alr-mutant strain. We found that biofilm formation, biofilm structure, and EPS synthesis was in a D-Ala dose-dependent manner. Biofilm structure was loose in alr-mutant group and the ratio of EPS/bacteria was also elevated. Additionally, the expression levels of multiple gtfs were up-regulated, and acid tolerance was decreased. We also established in vivo models of dental caries and found that the incidence and severity of the caries were decreased in the alr-mutant group in comparison to the parental S. mutans group. Our in vivo and in vitro experiments demonstrate that Alr is essential for the cariogenicity of S. mutans and that Alr might be a potential target for the prevention and treatment of caries.
丙氨酸消旋酶（Alr）已成为开发基于 D-Ala 参与细菌细胞壁生物合成的抗菌药物的新靶标。我们之前的研究指出，Alr 是变形链球菌生长和种间竞争力所必需的，变形链球菌是龋齿的主要致病原。然而，Alr 对变形链球菌的生理活性和致龋性的影响尚不清楚。本研究检测了 Alr 突变株的生物膜生物量、生物膜结构、胞外多糖（EPS）合成、葡糖基转移酶（gtf）基因表达、产酸和耐酸能力。我们发现生物膜形成、生物膜结构和 EPS 合成呈 D-Ala 剂量依赖性。Alr 突变株组生物膜结构疏松，EPS/细菌的比值也升高。此外，多个 gtf 的表达水平上调，耐酸性降低。我们还建立了龋齿体内模型，发现与亲本变形链球菌组相比，Alr 突变株组的龋齿发生率和严重程度降低。我们的体内和体外实验表明，Alr 是变形链球菌致龋性所必需的，Alr 可能是预防和治疗龋齿的潜在靶标。
