A STUDY OF THE BACTERIAL FLORA OF CARIES-SUSCEPTIBLE AND CARIES-IMMUNE SALIVA

¹ Dental Research Laboratory and Department of Bacteriology, Ohio State University, Columbus, Ohio

1. Quantitative comparison of gram-negative diplococci, gram-negative rods, yeasts, caseolytic organisms, streptococci, micrococci, and lactobacilli in caries-immune and caries-susceptible salivas showed that only lactobacilli occurred in significantly different numbers, being much lower in immune salivas.

2. An association of lactobacilli almost exclusively of smooth colony type with immune salivas was found, while susceptible salivas contained more rough than smooth lactobacilli.

3. Dissociation of colony morphology of a number of strains of lactobacilli was found to be influenced by the composition, pH, and physical state of laboratory media.

4. Immune saliva was found to have a greater inhibitory capacity for lactobacilli than susceptible saliva. Both salivas could induce variation of colony morphology of lactobacilli, but immune saliva also induced variation to a nonaciduric form which was less acidogenic than the parent culture.

5. The mechanism in immune saliva is apparently a selection, and is related to the process of inhibition in order of occurrence. The effects of immune saliva could account for the low numbers of lactobacilli compared to susceptibles, and possibly for the low caries rate of immunes by reduction of numbers and cariogenic potential of a part of the acidogenic flora.