Caries incidence in intact rats infected with Streptococcus sobrinus via transmission from desalivated cagemates.

The purpose of this study was to determine the influence of caging desalivated S. sobrinus-infected rats on the caries incidence in intact, previously uninfected cagemates. Weanlings were divided as follows: Stage I: Twenty desalivated animals paired with 20 intact animals (Group I); 20 intact animals paired with 20 intact animals (Group II). Animals were infected with S. sobrinus and fed diet 2000 and 10% sucrose water. After five weeks, ten paired animals from each group were killed. Desalivated animals had statistically higher (p less than 0.05) caries scores than did other animals. Stage II: The remaining Stage I infected animals from Groups I and II were paired with 40 new uninfected animals 15 days of age and fed cariogenic diets. After five weeks, new intact animals paired with Stage I desalivated animals had significantly higher smooth-surface enamel caries scores (38.0; SE 7.84) than new intact animals paired with Stage I intact animals (11.15; SE 3.69). Moreover, new intact animals caged for only five weeks with Stage I desalivated animals developed smooth-surface caries (38.0; SE 7.84) to a degree comparable with that in all Stage I intact animals in the experiment for ten weeks (36.6, SE 9.5; and 30.05, SE 4.1). The data suggest that desalivation may select a readily transmissible strain of S. sobrinus, which demonstrates enhanced virulence.