Studies of Changes in pH produced by Pure Cultures of Oral Micro-Organisms

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Abstract
The pH curves produced in a standard buffer soln. containing glucose were detd. for several oral micro-organisms at cell concs. of 1 to 33% by volume. Only at high cell concs. are the pH changes as rapid as those which occur in the microbic plaques on teeth. Furthermore, in only 1 of the 17 micro-organisms were the pH changes produced at different cell concs. proportional to the cell conc. A comparison has been made of the pH curves produced by pure cultures of different types of oral microorganisms at high cell cones. (33% by volume) with various carbohydrates, lactic acid and urea as substrates. The differences in the pH curves produced by different microorganisms suggest that, in addition to the ability of microorganisms to produce acid, the inability to consume acid and the inability to produce alkaline substances are also of importance in regard to the etiology of dental caries. Expts. on pH were performed with mixtures of oral lactobacilli and some other oral micro-organisms at high microbic cell concs. and with a limited amt. of substrate. Streptococci, yeasts and Sarcina prevented lactobacilli from reaching their lowest pH levels under these conditions.