MICROBIOLOGIC DIFFERENCES IN THE ORAL CAVITIES OF THE HUNT-HOPPERT CARIES-RESISTANT AND CARIES-SUSCEPTIBLE RATS

¹ Departments of Bacteriology, Zoology, and Chemistry, Michigan State College, East Lansing, Mich.

The oral microflora of caries-resistant and caries-susceptible rats was compared on many types of bacteriologic media. Differences in microflora between the two strains of rats were detected only by highly selective media for lactobacilli and streptococci, namely, tomato juice, LBS, and mitis salivarius agar.

Lactobacilli and Str. salivarius appeared more frequently in the caries-susceptible rats.

Lactobacilli were not detected until the rats were about 21 days old. The frequencies with which these organisms were recovered tended to increase as the susceptibles developed caries, in contrast to a decline in the resistant animals.

An unidentified streptococcus, which appeared as a rough, crateriform colony on mitis salivarius agar, was found in all the resistant rats which were examined and in 18 per cent of the susceptibles. The progeny of these susceptibles also exhibited this organism, which suggested that heredity may influence the types of microorganisms present in the mouths of rats.