Studies on isolation of Streptococcus mutans from the human tooth surfaces with or without caries

Abstract

Isolation experiments of Streptococcus mutans were conducted in 136 Japanese subjects in respect to the question of whether its incidence, isolated cell number and prevalency among the total streptococci are different between the caries-free tooth surfaces and carious lesions. By conducting several series of experiments, the following results were obtained.
(1) S. mutans could be isolated from both the materials of caries-free and -active tooth surfaces in 20 test individuals. However, the incidence (70%), number of cells (10^4.7) and prevalency (53%) of S. mutans in the materials of the caries-active surface were much higher than those of the caries-free surface (30%, 10^2.8 and 2.0%, respectively).(2) Isolation of S. mutans in 116 specimens from the occlusal, interproximal and smooth surfaces with or without caries of 87 persons were carried out. In caries free teeth, test materials as low as 0, 3 and 4 from 13 occlusal, 14 interproximal and 14 smooth surface specimens, respectively, were found positive for S. mutans. In contrast, with the carious lesions, 24 of 39 maetrials from the occlusal surface, 15 of 25 from the interproximal and 9 of 11 from the smooth were found positive. The number of S. mutansisolated (10^4.2 to 10^4.6) and its prevalency (42 to 56%) in carious lesions were also much higher than those (10^1.9-10^8.1 and 0.2-5.5%) of caries-free surface.(3) In the age-matched groups (7 or 8 years old in average), isolation of S. mutans from the materials of occlusal surface without caries or with caries of different grades C₀, C₁ or C₂ were carried out. Although no S. mutans were isolated from 13 specimns of thc caries-free surfaces, they were isolated from 18 of 34 C₀, 7 of 20 C₁ and 14 of 14 C₂ carious lesions. However, with C₀, C₁ and C₂ carious lesions, no significant differences in the isolated cell number and prevalency of S. mutans were observed.(4) More advanced carious lesions (C₃ and C₄) were examined for the prevalency of S. mutans in their materials. Although number of S. mutans in C₃ and C₄ lesions was much higher than those of C₀-C₂, their prevalencies were not different with other.
These results strongly suggest the possibility that the growth and establishmet of S. mutansin the dental plaque are ethiologically correlated with the caries development on the tooth surface, particularly in an early phase of caries induction. A possible mechanism of S. mutans in inducing the caries was discussed.
Studies of biological and biochemical properties of the isolates revealed that a majority of isolates from the tooth surface regardless of caries-free or-active are of semi-mucous (m) type which is capable of fermenting almost all carbohydrates tested but incapable of hemolysing the sheep red cells. Almost all the isolates of mucous (M) type which were infrequently isolated from the plaques showed an α hemolytic activity and some genetic defect in nature of fermenting the carbohydrates.