Streptococcus mutans Associated with Severe Dental Caries Induces Infective Endocarditis

Objectives: Streptococcus mutans, a major pathogen of dental caries, is considered to be a causative agent of infective endocarditis (IE). However, whether severe dental caries extending to the pulp space induced by that bacterium is a possible risk factor for IE remains unknown. In the present study, we evaluated the virulence of S. mutans for IE development using a rat model of simultaneous severe dental caries and heart valve injury.
Methods: Twenty rats (age 18 days) were fed a caries-inducing diet containing 56% sucrose until the end of the experimental period to induce severe dental caries. S. mutans strain SA31 (1×10⁶ CFU) was administered into the oral cavity of each once a day for 5 days for colonization in the oral cavity. At 3 months of age, heart valves in all rats were injured using a sterile catheter and wire under general anesthesia. Following that procedure, 7 rats were euthanized after 1 week, another 7 after 1 month, and the remaining 6 after 3 months. Then, S. mutans colonization in heart valves and the severity of dental caries in all rats were evaluated.
Results: The number of teeth affected by dental caries with pulp exposure were increased in the rats in a time-dependent manner. All rats with S. mutans isolated from a heart valve showed dental caries extending to the pulp space. In addition, the average number of tooth crowns with destruction below the gum line was significantly greater in rats positive for S. mutans heart valve infection as compared to those without such infection (P<0.01).
Conclusions: Our results suggest that S. mutans harbored in the oral cavity due to the presence of severe dental caries may be an important factor related to IE pathogenicity.
The study was supported by grants from JSPS KAKENHI (nos. JP18K09831 and 18K17254)