Elucidation of the caries-inducing mechanism by S.mutans and development of a diagnostic method to estimate caries-risk.

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Recentry, we have constructed S.milleri transformants KSB8, KSC43 and NH5 which individually express S.mutans gtfB,gtfC and gtfD coding GTF-I,-SI and -S enzymes, and established hybridoma which produce monoclonal antibodies mono-specific to the three GTFs. In this study, in vitro and in vivo cariogenicities of the three transformants were compared to elucicate the caries-inducing mechanism by S.mutans. Furthermore, using the mono-specific MAbs, a high-sensitive Gross-dot method for determination of the three GTFs was developed. The results obtained were as follows :1. More stable gtfC-expressing transformant KSC43-RT was reisolated from an oral cavity of rat infected with KSC43.2. In vitro cariogenicity of the transformants was examined by a colonization test. The results showed that only KSC43-RT cells could makedly colonized on glass surfaces.3. In vivo cariogenicity of the transformants was tested by a rat model system. The results showed that the KSC43-RT cells could induced the buccal and sulcal caries, and the KSB8 cells could induced the proximal caries, but the NH5 cells did not.4. High-sensitive Gross-dot assay method was established and applied in order to evaluate the cariogenicity of S.mutans strains.5. Cell-associated GTFs from various clinical isolates of S.mutans were analyzed by the method. The results showed that the levels of three GTFs and those ratio were markedly different among the isolates.These results suggest that the gtfC product was especially important for caries development caused by S.mutans, and that the high-sensitive Gross-dot method may be useful to estimate the exact cariogenicity of individual strain of S.mutans.