Characterization of a Large Amount of Water-insoluble Polysaccharide Synthesis Streptococcus salivarius

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The cariogenicity of a large amount of insoluble polysaccharide synthesis isolate from the human oral cavity on Mitis Salivarius agar was investigated. The isolate was identified as Streptococcus salivarius subsp. salivarius by genetical and biochemical analysis and was designated the NUM 6069 strain. NUM 6069 produced a large amount of water-insoluble polysaccharide from sucrose, and the plaque formation of the NUM 6069 strain was also strong ; however, no adherent or sticky plaques were observed. Acid production of NUM 6069 from glucose was rapid. The time taken to critical pH in the strain was faster than in the S. salivarius subsp. salivarius type strain JCM5707T and was similar to that in S. mutans. Expression of mRNA of the NUM 6069 ftf gene increased 42-fold compared to that of JCM5707T. All gtf genes, gtfJ, gtfK, gtfL and gtfM of NUM 6069 increased 2- to 6-fold compared to those of JCM5707T. In in vivo experiments, the caries scores and bacterial colonization of the NUM 6069 infected group were obviously decreased compared to those of the S. mutans infected group. These results reconfirm that sticky water-insoluble polysaccharides are important in the induction of dental caries.