Study on Streptococcus mutans sucrose-dependent adherence and cariogenesis.

当变形链球菌附着在牙齿表面时，它开始增殖并形成生物膜，由蔗糖合成水溶性和非水溶性葡聚糖。已知这些葡聚糖由gtfB / C / D基因编码的GTFB / C/ D三种葡糖基转移酶合成，并被dexA基因编码的葡聚糖酶（DexA）降解。S.龋损中的变形菌可调节葡聚糖代谢以适应细胞周围的微环境。本研究的目的是探讨S.当环境发生变化时，生物膜或牙本质小管中的变形菌。我们建立了一种由牛牙本质切片和S.变异株或缺陷突变株。牙本质切片和S.在不同条件（温度、pH或蔗糖浓度）下孵育变形杆菌。用PCR方法检测gtf基因和dexA基因的表达。S.粘附于牙本质板的变形菌MT（野生型）不因环境变化而减少，而非粘附细胞的减少。贴壁细胞的gtf基因表达水平高于未贴壁细胞。此外，gtfC基因在贴壁细胞中表达最高。透射电镜和光镜观察表明，S.在该模型中，变形菌侵入了牛牙本质的大部分牙本质小管。当培养条件改变时，细胞开始合成胞内多糖。gtfC基因缺陷型菌株产生的WIG粘附在牙本质板上的量低于其他基因缺陷型菌株。这些结果表明S.粘附于牙齿表面的变形菌通过合成葡聚糖或通过适应环境变化来改变GTF和DexA的量。

When Streptococcus mutans adheres to the surface of teeth, it begins to proliferate and form biofilm synthesizing the water-soluble (WSG) and -insoluble glucan (WIG) from sucrose. It is well known that these glucans are synthesized by three kinds of glucosyltransferases, GTFB / C / D, coded by gtfB / C / D gene, and are degraded by dextranase (DexA) coded by dexA gene. S. mutans in carious lesions may modulate glucan metabolism to adapt to the micro-environment surrounding cells. The purpose of this study was to investigate the ecological changes of S. mutans in biofilm or dentinal tubules when the environmental changes occur. We developed an in vitro artificial carious model composed of bovine dentin slices and S. mutans or deficient mutant strains. Dentin slices and S. mutans were incubated under vaious condition (temperature, pH or concentration of sucrose). The expression of gtf genes, and dexA gene were examined using PCR method. The growth rate of S. mutans MT(wild type) adhered to a dentin plate was not reduced by the environmental changes, while that of non-adhered cells decreased. The levels of gtf gene expression of adhered cells were higher than those of non-adhered cells. Moreover, gtfC gene showed the highest expression in adhered cells. TEM and LM observation revealed that S. mutans invaded most of dentinal tubules of bovine dentin in this model. When the culture condition was changed, the cells began to synthesize the intra-cellular polysaccharide. The gtfC deficient mutant strain produced lower amount of WIG that was adhered to the dentin plate compared with other gene deficient mutants. These results suggest that S. mutans adhered to the tooth surface changes the amount of GTFs and DexA, by synthesizing the glucan, or by adapting to the environmental changes.