Molecular analysis of cell surface structures of Streptococcus mutans for virulence of infective endocarditis

从感染性心内膜炎患者血液中分离出的不可血清分型的突变链球菌被命名为新型k血清型。该血清型菌株的特点是在血清型特异性多糖中鼠李糖主干上的葡萄糖侧链急剧减少。血清k型菌株一般不太容易龋齿，但由于对多形核白细胞吞噬的抵抗，它们诱导的菌血症持续时间较长。对参与血清型特异性多糖生物合成的基因进行了测序，发现存在血清型k菌株共有的特异性区域。利用该区域的核苷酸，构建了快速鉴定血清型k株的PCR方法。通过插入失活编码各蛋白的基因，获得了具有主要表面抗原缺陷的等基因突变株。体外和大鼠菌血症模型实验表明，蛋白抗原（PA）和葡聚糖结合蛋白C （GbpC）参与了突变链球菌在血液中的毒力。此外，生物膜调控蛋白A （BrpA）的失活导致更长的链形成，从而增强了血小板的聚集特性。利用心脏瓣膜和心血管手术中取出的热斑标本提取的DNA进行口腔细菌PCR检测。与牙周炎相关的细菌种类被确定，然而，突变链球菌的检出率远远高于这些物种。此外，S.突变体在心血管标本中的血清型分布与在口腔标本中的完全不同。这些结果表明，葡萄球菌突变体可能与心血管疾病有关。

The unserotypeable Streptococcus mutants strains isolated from blood of the patients with infective endocarditis was designated as novel serotype k. The serotype k strains is featured with the drastic reduction of the glucose side chains attached to the rhamnose backbone in the serotype-specific polysaccharide. The serotype k strains were shown to be generally less cariogenic, while they induced longer duration of bacteremia due to the resistance to phagocytosis by polymorphonuclear leukocytes. The genes involved with the biosynthesis of serotype-specific polysaccharide were sequenced, which revealed the existence of the specific region common in serotype k strains. Using the nucleotides of this region, the PCR method for rapid identification of the subjects with serotype k strains was constructed.The isogenic mutant strains with the defect of major surface antigens of S. mutants were generated by insertional inactivation of the genes encoding each protein. The in vitro and rat bacteremia model experiments showed that protein antigen (PA) and glucan-binding protein C (GbpC) were involved with the virulence of S. mutants in blood. In addition, inactivation of the biofilm regulatory protein A (BrpA) resulted in the longer chain formation, which enhanced the platelet aggregation properties.PCR detection of oral bacteria using the DNA extracted from heart valve and athermatous plaque specimens extirpated in the cardiovascular operations has been carried out. The bacterial species involved with periodontitis was identified, however, the detection rate of S. mutants was extremely higher than these species. Furthermore, the serotype distribution of S. mutants in cardiovascular specimens was shown to be totally different from that in the oral cavity. These results indicate that S. mutants is possibly associated with the cardiovascular diseases.