Streptococcus mutans 6715 ribosomes disrupted in a Braun homogenizer were isolated in sodium dodecyl sulfate by differential centrifugation. This preparation contained 80% RNA and 20% protein, and carbohydrate was not detected by phenol-sulfuric acid and methyl pentose assays. The sedimentation coefficient of the ribosomes was 70S. After dialysis in 0.01 M phosphate buffer containing 10(-4) M MgCl2, the ribosomes dissociated into 54S and 32S particles. Leukocytes from rabbits immunized intramuscularly with the ribosomal preparation showed transformation and migration indices of 13.0 and 0.71, which were significantly different (P less than 0.05) from the respective indices of 0.9 and 0.98 in nonimmunized animals. Hyperimmune serum from these rabbits agglutinated representative Formalin-killed strains of all seven serotypes of S. mutans, inhibited adherence of live S. mutans 6715 to glass, and agglutinated S. mutans 6715 ribosomes adsorbed upon erythrocytes. These findings suggested that animals immunized with S. mutans ribosomes may be protected from caries caused by any of the seven serotypes of this organism.
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