著者

藤坂 菊美

出版者

徳島大学

雑誌

四国歯学会雑誌 (ISSN:09146091)

巻号頁・発行日

vol.20, no.1, pp.61-74, 2007-06

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Genetic competence in S. mutans is regulated by a quorum-sensing system mediated by a competence-stimulating peptide (CSP). CSP encoded by the comC gene is involved in competence for genetic transformation and biofilm formation. The quorum-sensing system in S. mutans involves four gene products encoded by comC, comD, comE and comX. The comC, comD and comE genes encode a CSP precursor, its histidine kinase sensor protein, and a cognate response regulator, respectively. The loci of comC and comDE lie adjacent on the chromosome. comX encodes a sigma factor, however little is known about the influence that the quorum-sensing system has on the pathogenicity of S. mutans. It is of interest to verify the roles of the quorum-sensing system in S. mutans for its ability to form a biofilm. To test this hypothesis, S. mutans wild-type strain UA159 and its knockout mutants, which were defective in comC, comD, comE and comX mutant, were examined for their ability for initial adhesion, glucan synthesis and invasion into dentinal tubles. The initial adhesion ability of S. mutans cells to saliva-coated hydroxyapatite was decreased in comD and comE mutant strains. This result shows that the quorum-sensing system already has an influence on initial biofilm formation to be adherent or the early phase of carious formation. 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, comD, comE and comX mutant increased more than by the wild type when cultured in brain heart infusion for 24 days. This study demonstrated that the quorum-sensing system may play a crucial role in initial adhesion, glucan synthesis, biofilm formation and invasion to dentinal tubules of S. mutans.