Construction and Isolation of streptococci useful for caries-prevention by replacement therapy

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Mutans streptococci, Streptococcus mutans and Streptococcus sobrinus, have been considered the principal etiological agents of dental caries. The degree of colonization of these organisms correlates with the prevalence of dental carries in, human and experimental animals. An important virulence factor of mutans streptococci promoting caries development is the abilities to colonize firmly to the tooth surface in the presence of sucrose and produce the cariogenic biofilm in situ.The purpose of this research project was to construct or to isolate anti-cariogenic I streptococci useful for caries prevention by replacement therapy. The results have shown that a S. mutans MKM33 isolated from a caries-free student was colonizable and non-cariogenic in rats, that two S. sobrinus like isolates (HG1006 and HG988) from Dutch childs were identified as S. cricetus and both isolates also were colonizable and non-cariogenic in rats, and that a S. gordonii transformant expressing a cyclodextran-synthesizing enzyme gene was colonizable in mice. These findings suggest that the clinical isolates. MKM33, HG1006 and HG988 might be useful for caries prevention by replacement therapy. In addition, some useful microbiological methods for isolation of mutans streptococci were established, and many S. mutans were isolated from students with zero or low of caries experience, but S. sobrinus did not.