Study on synthesizing of intracellular polysaccharide by Streptococcus mutans in dentinal tubules.

变形链球菌是一种由蔗糖合成水溶性葡聚糖（WSG）和水不溶性葡聚糖（WIG）的致龋细菌，附着在牙齿上增殖。本研究检测了变形链球菌野生型菌株UA159及其敲除突变体comC、comX和scrA突变体的初始粘附能力、葡聚糖合成能力和侵入牙本质小管的能力。所有突变株的水不溶性葡聚糖合成比例均低于野生型。水溶性葡聚糖粘附在牙本质薄片上的比例也均低于野生型。三种葡聚糖组合物的总剂量在所有突变株中均降低。comC和comX突变体在脑心灌注培养24 d后，牙本质小管的扩张率明显高于野生型。野生型和scra突变体之间的生长没有可检测到的差异。蔗糖存在时，scra突变体WSG和WIG的产量低于野生型。本研究表明，群体感应系统和PTS系统可能在变形链球菌的葡聚糖合成、生物膜形成、胞内多糖的产生和对牙本质小管的侵袭中发挥重要作用。

Streptococcus mutans that is one of the cariogenic bacterium is synthesized the water-soluble glucan (WSG) and the water-insoluble glucan (WIG) from sucrose, adheres on the tooth, and proliferates. In this study, S. mutans wild-type strain UA159 and its knockout mutants, which were defective in comC, comX and scrA mutant, were examined for their ability for initial adhesion, glucan synthesis and invasion into dentinal tubles. The proportions of water-insoluble glucan synthesis in all mutant strains were less than the wild type. The proportions of water-soluble glucan adhering to dentin slices in all mutant strains were also less than in the wild type. The total dose of three kinds of glucan composition decreased in all mutant strains. The expansion rates of dentinal tubules by comC and comX mutant increased more than by the wild type when cultured in brain heart infusion for 24 days. There were no detectable difference in growth between wild-type and scrA-mutant. In the presence of sucrose, the produce of WSG and WIG in scrA-mutant was less than in wild-type. This study demonstrated that the quorum-sensing system and PTS system may play a crucial role in glucan synthesis, biofilm formation, production of intracellular-polysaccharide and invasion to dentinal tubules of S.mutans.