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Streptococcus mutans (PK1, GS5, HS6, Ingbritt m type, N type, and 102-2), Neisseria and Streptococcus salivarius were examined for their growth in liquid media, their adherence to the surface of the glass and their agglutination reaction in the presence of different carbohydrates. They were then inoculated orally into germfree JCL: ICR mice which were fed on diets with or without containing 50% different carbohydrates. Their growth on the surface of the tooth and their ability to form dental plaques were compared with their in vitro properties of growth and adherence. The following results were obtained.(1) All the strains tested showed an abundant growth when cultivated in Trypticase Yeast (T. Y.) medium fortified with sucrose, glucose or fructose, but no growth was observed when cultivated with medium containing no carbohydrates. (2) All the strains except S. mutans N type, showed the adherence of organisms to the glass wall of the culture bottle that contained the TV-broth fortified with sucrose. No adherence were observed with medium that contained other carbohydrates. The agglutination of organisms was also observed with all the strains when tested in the presence of sucrose but not with glucose or fructose. However, S. mutans PK1 showed the most potent ability in both reactions among the strains tested. (3) Among those tested for the infection of the germfree mice, S. mutans PK1 was found to exhibit the most potent capability to form dental plaques. The mice, when inoculated with the PK1 strain and fed diets containing 50% sucrose, showed the following mean staining indices of plaque of 7.3, 26.1 and 59.2 at 2nd, 4th and 8th week, respectively. While the staining indices of the uninfected mice ranged between 1.4 and 2.8 In the mice fed with diets containing 50% glucose or fructose, PK1 grew well as did the organisms in mice fed with sucrose-diets but showed much less indices of plaque formation. (4) S. salivarius also grew well on the tooth surface in germfree. mice but showed only a slight plaque formation to the similar levels as those in uninfected mice even when fed with 50% sucrose diets. (5) S. mutans 102-2 strain, which exhibited the carbohydrate-dependent growth in vitro and the adherence properties similar to those of PK1 strain, did not grow well on the surface of the tooth and so produced a very low plaque index either when fed diets with sucrose or without sucrose. This phenomenon suggested that this strain may be genetically unable to grow in JCL: ICR mice.In conclusion, a strain (S. mutans PK1) which can firmly adhere to the surface of the glass in the medium containing sucrose could grow on the surface of the tooth and form thick dental plaques on it. In contrast, a strain (S. mutans 102-2) which can also firmly adhere to the surfaces of the glass could not grow on the tooth and therefore showed no potent capability to make a plaque. S. salivarius which can adhere to the glass and produce levan but not glucan could grow on the tooth but showed no potent sucrose-dependent plaque formation. Thus, the experimental model of plaque formation by S. mutans in the germfree mice presented in this report may provide us a valuable method to evaluate the role of the dental plaque on periodontal diseases and on dental caries.

Dental Plaque Formation in Gnotobiotic and Germfree Mice