STUDIES ON THE NUMBERS OF BACTERIA IN THE MOUTH AND THEIR REDUCTION BY THE USE OF ORAL ANTISEPTICS

¹ Department of Bacteriology, University of New Hampshire, Durham, N. H., and Department of Medicine, Tufts Medical School, Boston, Mass.

Tryptose glucose blood agar was found to be an excellent medium for the quantitative estimation of the oral bacteria since it affords counts on oral streptococci as well as other general types of mouth organisms. Tomato juice agar adjusted to pH 5.0 was suitable for the estimation of oral lactobacilli.

A paraffin-saliva technic similar to that described by Hadley¹ was found to be superior to a brushing and rinsing technic for the collection of representative samples for determining numbers of bacteria in the mouth. The collection of saliva over a three-minute chewing period appeared to be as satisfactory for obtaining representative samples as a shorter or longer period. However, we feel that quantitative estimation of numbers of lactobacilli or other bacteria in the mouth should be based on total numbers of bacteria collected in the samples and not on the numbers per ml. of saliva as has been done by most investigators in the past.

The fluctuation in numbers of bacteria in the mouth at ten different periods during the day was indicated. The numbers generally decreased onehalf to one hour after each meal. The largest numbers were usually found early in the morning, at noon, and late in the evening.

Under the conditions of the test, glycerite of hydrogen peroxide (0.75 per cent, 0.5 per cent, and 0.37 per cent) and Cepacol generally produced a continual reduction in the oral bacterial flora when used twice daily as a mouth rinse. A very marked reduction in the numbers of oral bacteria was obtained when two or three penicillin troches (5000 units) were dissolved in the mouth daily, the streptococci being reduced in numbers over 99 per cent.