抄録
Streptococcus mutans, consisting of serotypes c, e and f is an oral aciduric organism associated with the initiation and progression of dental caries. Recently a new serotype k S. mutans was proposed. The distribution of serotype k S. mutans was investigated in 244 subjects. The ratio of S. mutans and Streptococcus sobrinus against total streptococci was approximately 1-0.1%. Mutans streptococci were found in 212 subjects (86.9%), S. mutans in 74.2% and S. sobrinus in 12.7%. No mutans streptococci were found in 32 subjects (13.1%). The predominant serotype was c with 84.9% detection in S. mutans. Serotype k was found in only 3 subjects (1.4%) : 1 of them had a coexisting serotype c strain and the other 2 were alone. Serotypes d and g of S. sobrinus were detected at equal percentages and those usually coexisted with S. mutans strains. Serotype k S. mutans isolates were confirmed by serological and genetical methods and characterized. The homologies of the rgpF gene sequence, which is related to the biosynthesis of serotype antigens, of isolates were 93-100% among serotype k type strains and 71% with serotype c to serotype k strains. Water-insoluble glucan synthesis from sucrose and artificial plaque formation of the serotype k strains were similar to those of the serotype c strain. However, acid production by the serotype k strains was comparatively lower than that of serotype c. A few years after the first investigation, serotype k S. mutans was confirmed to be maintained in the individual oral cavities of the same subjects by genetic analysis.
