ACID PRODUCTION OF ORAL BACTERIA ASSOCIATED WITH DENTAL CARIES

¹ Hygienic Laboratory, University of Michigan, Ann Arbor, Michigan

The acidogenic and aciduric properties of 30 strains each of oral lactobacilli, streptococci, staphylococci, and yeast-like organisms were tested. All strains produced a terminal pH of 5.0 or less in glucose broth, but the lactobacilli alone lowered the hydrogen-ion concentration markedly below this level. On the basis of subculture after 10 days in glucose broth all except the streptococci could be considered aciduric; only 2 of the 30 strains were capable of being subcultured at the end of this period. In brom-cresol-green dextrose agar (pH 4.75) neither the streptococci nor yeast alone or in combination changed the color in 4 days. A few strains of staphylococci gave positive reactions in 48 hours.

However, 29 of the 30 strains of lactobacilli turned the medium in 24 hours or less. Symbiotic mixtures gave no indication of increased acid production under the conditions of the experiment.