A SIMPLE COLORIMETRIC METHOD FOR THE ESTIMATION OF RELATIVE NUMBERS OF LACTOBACILLI IN THE SALIVA

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

Changes in color in selected time intervals of brom-cresol-green glucose or lactose infusion agar (pH 5.0) in "shake" tubes after inoculation of 0.1-0.2 c.. of saliva were correlated with quantitatively estimated numbers of lactobacilli in the respective specimens. It was found possible to select by negative color change in 48 hours with 4 per cent error those specimens having less than 1000 lactobacilli per c.c. of saliva, but it became increasingly difficult to interpret color shifts directly in terms of lactobacilli in the saliva. The possibility of direct application in the study of dental caries is discussed.