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到的不能分型的链球菌突变株被命名为新的k型。该k型菌株的特征是附着在血清型特异性多糖中鼠李糖骨架上的葡萄糖侧链急剧减少。血清型k型菌株的致龋性一般较低，但由于多形核白细胞对吞噬的抵抗，它们引起的菌血症持续时间较长。对与血清型特异性多糖生物合成相关的基因进行了测序，发现k型菌株存在共同的特异区。利用该区域的核苷酸序列，建立了快速鉴定k型菌株的聚合酶链式反应方法，通过插入失活编码各蛋白的基因，获得了具有突变株主要表面抗原缺陷的同源突变株。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)与血液中突变链球菌的毒力有关。此外，生物膜调节蛋白A(BrPA)的失活导致更长的链形成，从而增强了血小板的聚集性。从心血管手术中取出的心脏瓣膜和动脉粥样硬化斑块标本中提取的DNA进行了口腔细菌的PCR检测。对与牙周炎有关的细菌种类进行了鉴定，但突变菌株的检出率极高。此外，心血管标本中突变链球菌的血清型分布与口腔中的完全不同。这些结果表明，突变株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.