Potentially cariogenic microorganisms cultured from noncarious and carious root and coronal (enamel) surfaces were quantitatively compared in patients 22 to 84 years of age (mean, 52 years). We collected 150 plaque specimens from 26 in situ teeth with initial root lesions and from 25 extracted teeth with advanced root lesions. The frequencies of isolation of Streptococcus mutans, Actinomyces viscosus, and Lactobacillus spp. were, respectively, 94, 72, and 51% at the noncarious root site; 98, 71, and 54% at the root lesion; 84, 61, and 44% at the noncarious enamel site; and 100, 66, and 90% at the enamel lesion. The streptococci made up the largest mean proportion of the total anaerobic cultivable microflora, ranging from 31.2% at the noncarious enamel site to 37.6% at the root lesion, while S. mutans varied between 18% at the noncarious enamel and root surfaces and approximately 24% at both the enamel and root lesions. The proportion of actinomyces ranged from 12.3% at the root lesion to 23.6% at the noncarious root site, while A. viscosus varied from 7.8% at the root lesion to 15.1% at the noncarious root site. The largest mean proportion of lactobacilli (4.2%) was recovered at the enamel lesion site. Proportions of Candida spp. made up less than 0.1% at all sites. Proportions of microorganisms did not differ significantly between noncarious enamel and root sites, but the noncarious coronal and root sites had higher (P less than 0.05) proportions of actinomyces than did the root lesion. Also, enamel lesions had a greater (P less than 0.05) percentage of Lactobacillus spp. than did root lesions. The number of streptococci recovered from the root lesion was greater (P less than 0.01) than the number of actinomyces at the same site. S. mutans was recovered from initial root lesions in greater numbers (P less than 0.001) than were actinomyces and lactobacilli. The number of S. mutans recovered at the initial root lesions was greater (P less than 0.01) than that recovered from the advanced root lesions.

Scanning and light microscopy reveals a selective and restrictive pattern of indigenous bacterial colonization on the tongue of rats which is accounted for by the preferred attachment of bacteria to an "intermediate soft" keratin substrate. Total intravenous feeding of rats for 10 days did not alter this colonization pattern indicating that oral intake of food is not responsible for maintenance of this pattern.

Three strains of anaerobic, dextranase-producing, gram-positive, rod-shaped bacteria were isolated from human dental plaque associated with root carious lesions. The isolates produced a molar ratio of acetate to lactate from glucose fermentation ranging from 1.1 to 1.9. Each strain also produced fructose-6phosphate phosphoketolase. The isolates were identified as belonging to the genus Bifidobacterium, but from their carbohydrate fermentation patterns they did not appear to be strains of Bifidobacterium dentium. These microorganisms fermented high-molecular-weight dextrans. A partial characterization of the dextranase activity was included in this study and revealed an extracellular dextranase with a pH optimum of 7.1. Analysis of the dextran degradation products demonstrated the liberation of saccharides larger than 1 glucose unit. It was concluded that this enzyme used an endohydrolytic mode of dextran cleavage.

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