Resolution of quorum-sensing systems in dental plaque biofilm and development of the method that prevents the plaque formation by the control of them

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Dental plaque is the biofilm which is formed on the tooth surface, and is a protective barrier for the bacteria against the change of the environment, the antibiotic, and the host immune response. First this biofilm is formed by the extracellular polysaccharide (glucan), which the mitis group streptococci produce from sugar, and then is reinforced by the adhesive and water-insoluble glucan, which the mutans group streptococci produce. Dental plaque biofilm plays an important role in the caries formation. In this biofilm, the plaque bacteria communicate with other bacteria by the auto-inducer like hormone. By this communication system that is commonly known as quorum-sensing, the bacterial population density in the dental plaque is thought to be kept constant, and the bacterial mass against the host immune system is constructed.In the present study, to solve the quorum-sensing system in the dental plaque, we developed the method to identify the oral streptococci, which were the members of this biofilm. This method could rapidly identify the streptococci which were dominant and occupied 60% in the oral flora. We published the paper about it entitled "Method for rapid identification of oral streptococci by PCR using 16S-23S ribosomal RNA intergenic spacer". On the other hand, we investigated the longitudinal study of oral flora against the 2 predentate infants and the cross-sectional study of oral flora against the 40 nursery school students (aged 1 to 4 years old). As a result, we demonstrated that the rate of alpha-hemolytic bacteria in oral flora decreased by the inhabitation of the mutans streptococci, suggested that the quorum-sensing system between mutans streptococci and alpha-hemolytic bacteria existed. We had submitted the paper about this entitled "Establishment of S.mutans Change Salivary Bacterial ratio".Our future study is to identify auto-inducer produced between mutans streptococci and alpha-hemolytic bacteria.