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

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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.