Oral implantation and the cariogenic activity of clinical strains of Streptococcus mutans which had been isolated from Japanese children and labeled with streptomycin-resistance were examined in specific pathogen-free Sprague-Dawley rats. All the seven strains tested were easily implanted and persisted during the experimental period. Extensive carious lesions were produced in rats inoculated with clinical strains of S. mutans belonging to serotypes c, d, e, and f, and maintained on caries-inducing diet #2000. Noninfected rats did not develop dental caries when fed diet #2000. Type d S. mutans preferentially induced smooth surface caries in the rats. Strains of other serotypes primarily developed caries of pit and fissure origin. Caries also developed in rats inoculated with reference S. mutans strains BH-TR and FAlR (type b) that had been maintained in the laboratories for many years. However, the cariogenicity of the laboratory strains was found to have decreased markedly. All three S. sanguis strains could be implanted, but only one strain induced definite fissure caries. Two S. salivarius strains could not be implanted well in the rats and therefore they were not cariogenic. Four different species of lactobacilli also failed to induce dental caries in rats subjected to similar caries test regimen on diet #2000. S. mutans strain MT6R (type c) also induce caries in golden hamsters and ICR mice, but of variable degrees.

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SUMMARY: Purified cell walls of Actinomyces viscosus and Actinomyces naeslundii were solubilized by the enzymatic action of M1 N-acetylmuramidase . Soluble cell wall carbohydrate antigens were purified by column chromatography . A purified antigen preparation (fraction C) from A. viscosus ATCC 19246 was found to contain deoxyhexoses (rhamnose and 6-deoxytalose), hexosse (galactose , glucose and mannose), and a peptidoglycan component.This preparation gave a single precipitin band against antiserum to homologous whole cells. Similar antigen preparations were purified from M1 enzyme lysate of A, viscosus SK4 and A. naeslundii ATCC 12104 cell walls.