Development of a caries risk assessment system using genetic polymorphisms influencing cariogenicities of mutans streptococci.

变形链球菌被认为与龋齿密切相关。据报道，携带这种细菌的儿童龋齿患病率和发展明显较高。变形链球菌可以通过合成葡聚糖在牙齿表面定植和积聚。在变异链球菌的三种葡萄糖基转移酶中，由gtfB基因编码的GTF-Ⅰ是合成水不溶性葡聚糖（WIG）的最重要的酶。为探讨gtfB基因多态性与WIG合成之间的关系，收集了小学生石蜡刺激唾液，从这些唾液样本中分离出21株变形链球菌临床菌株。结果表明，GTF-Ⅰ的gtfB基因在409-427位有ANDVDNSNPVVQAEQLNWL（19个氨基酸），在446-454位有DSIRVDAVD（9个氨基酸），这些序列对GTF-Ⅰ的酶活性非常重要。在gtfB的3 '端有直接的重复单元，是葡聚糖结合结构域。在本研究中，发现临床分离株中gtf B编码区和酶催化位置（409-427和446-454）之前的序列是高度保守的，并且一些WIG合成低的菌株在GTF-I的C-末端具有直接重复单元的缺失。

Streptococcus mutans is considered as strongly associated with dental caries. It was reported that children carrying this bacteria had significantly higher caries prevalence and development. S.mutans can colonize and accumulate on the tooth surface by glucan synthesis. GTF-I coded by gtfB gene is the most important enzyme on water-insoluble glucan (WIG) synthesis among three glucosyltransferase of S.mutans. The aim of this study was to investigate the association between genetic diversity of gtfB and WIG synthesis.We collected paraffin-stimulated saliva from primary schoolchildren, and 21 clinical strains of S.mutans were isolated from these saliva samples. Base sequences of gtfB of these strains were determined by direct sequencing analysis.In these days, it was revealed that GTF-I has ANDVDNSNPVVQAEQLNWL (19 aa) at 409-427 and DSIRVDAVD (9 aa) at 446-454, and these sequences are very important for enzyme activity of GTF-I. There are direct repeating units in 3'-terminal of gtfB, which are glucan binding domain. This repeating units are also important for glucan synthesis.In this study, it was revealed that the sequence preceding the coding region of gtf B and enzymatic catalysis position (409-427 and 446-454) are highly conserved among the clinical isolates and that some strains whose WIG synthesis are low have deletion of direct repeating units in C-terminal of GTF-I.