本研究では感染性心内膜炎(infective endocarditis:IE)発症における口腔内細菌の関与について検索した.IE 患者47 名の血中から検出された細菌の87.1%は口腔細菌であり,61.7%の患者が口腔内感染巣を有するか,抗菌薬予防投与なしで口腔内観血処置が施行されていた.また,IE 患者あるいはIE 発症リスク患者の27 名の口腔細菌(連鎖球菌とブドウ球菌)の薬剤感受性を検索したところ,92.3%はペニシリン系薬剤に対して感受性を示した.さらに,I E 患者9 名において血中細菌と口腔細菌の16S rRNA の遺伝子配列を決定することにより細菌種の同定を行った.その結果,血中から検出・同定された細菌は全て口腔に存在するStaphylococcus epidermidis とStreptococcus mitis group であった.また,血中細菌と口腔細菌の遺伝子配列は1 症例で100%一致し, 3 症例においては遺伝子配列の100%の一致は見られなかったが,細菌種グループまでは一致した.以上の結果より,IE 発症には口腔内の連鎖球菌とブドウ球菌が原因菌として重要であることが明らかとなった.また,IE 発症の予防には,口腔内感染巣の除去と日々の口腔ケアならびに口腔内の観血処置時には大量のペニシリン系薬剤の予防投与は有用であることが確認できた.In this study, we attempted to clarify the implication of the oral bacteria on the onset of infective endocarditis( IE). In the first experiment, oral bacteria could be found in the blood from 27 of the 47 patients( 57.4%) with IE. Furthermore, 29 of the patients( 61.7%) showed possible oral bacterial foci causing the bacteremia, and 8 of the patients (17.0 %) received the oral surgery or the dental treatment accompanying bleeding. In the second experiment, we isolated the oral bacteria( Staphylococci and Streptococci) from the 27 patients with IE or with high risk for the onset of IE, and determined the susceptibility for several anti-biotics. Ninety two point three percent of the bacteria showed susceptibility against penicillin G and its derivatives. In the third experiment, we identified the bacterial species isolated from oral cavity and blood in nine patients with IE by determining the DNA sequence of the 16S rRNA. The bacterial species isolated from blood in the patients with IE were Staphylococcus epidermidis or Streptococcus mitis group, which usually existed in the oral cavity. DNA sequence of the 16S rRNA in the bacteria( Staphylococcus epidermidis) from blood in one patient was completely identical to that from oral cavity. In three patients, although DNA sequence from blood was not completely identical to that from oral cavity, the species( Streptococcus mitis group) of the bacteria from blood and oral cavity were identical. These results suggest that oral Staphylococci and Streptococci play a crucial role on the onset of IE. Moreover, complete removal of the oral bacterial foci, daily oral care, and the administration of the large amount of penicillin before the oral surgery or the dental treatment accompanying bleeding might be effective to prevent the onset of IE
