Experimental infective endocarditis induced by human supragingival dental plaque

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Human dental plaque, which consists of numerous species of microorganisms, is thought to work as a pathogen not only in the oral cavity but also in other body sites. However, the pathogenicity of human dental plaque itself in systemic disease is not fully examined. The ability of human supragingival dental plaque to induce infective endocarditis was examined using the rat model. The bacteria were isolated from the locus of infection and the ability of the isolate to induce endocarditis was evaluated. In total, 15 out of 27 catheterized rats survived after intravenous injections with human supragingival dental plaque suspensions containing 3×10^6 CFU of bacterial cells In surviving rats, infiected vegetations were formed in all except one rat. The microbial composition of the infected vegetations was very simple compared to the respective dental plaque inoculates. In all infected vegetations examined, Streptococcus oralis comprised the majority of the isolates. In rats affected with infective endocarditis, the aortic sinus was filled with fibrinous vegetation containing bacteria. Numerous inflammatory cells infiltrated the aortic valve and the aorta adjacent to the valve. A cell suspension of S.oralis isolated from the infected vegetation was capable of inducing endocarditis lesions in all catheterized rats when inoculated at 5×10^6 CFU per rat. The results suggest that human supragingival dental plaque is an important source of dissemination of pathogen, which causes infective endocarditis.