Two rhein-metabolizing bacteria were isolated from human feces. The biochemical and morphological characteristics of both isolates were typical of Bacteroides spp. and named strains RHEIN-I and RHEIN-II, respectively. Rhein was effectively metabolized to rheinanthrone by both strains. In conventional male Wistar rats, diarrhea was not induced after oral administration of rhein at a dose of 100 mg/kg (fecal water content of 71 %), in spite of severe diarrhea with sennoside B at a dose of 40 mg/kg (increase of fecal water content to 89 %). Also in germ-free rats, rhein did not induce any diarrhea. Gnotobiote rats colonized with B. sp. strain RHEIN-I developed diarrhea (fecal water content increased to 85 %) 11 hr after the oral administration of rhein. These findings indicate that rhein-transforming bacteria are responsible for the laxative effect associated with the ingestion of rhein and rhein containing preparations. rhein, rheinanthrone, diarrhea, Bacteroides, gnotobiote.
ヒト糞便から2種のrhein代謝細菌を単離した。これらは生化学的および形態学的特徴からBcteroidesに属する種と判断され,RHEIN-I,RHEIN-II株と仮称した。rheinは両菌株により完全にrheinanthroneに代謝された。通常の雄Wistarラットにおいてはrhein 100mg/kgの経口投与で下痢が生じなかったが(糞便の水分含量は71%),sennoside Bでは40mg/kgの用量で激しい下痢を生じた(水分含量89%)。又,無菌ラットではrheinは何ら下痢作用を示さなかった。ところが,Bacteroides sp. strain RHEIN-Iを消化管内に棲息させたラットではrhein経口投与の11時間後に下痢が生じた(糞便の水分含量は85%)。この結果は,これらrhein代謝菌がrheinやrheinを含む製剤を摂取した場合に生じる下痢作用に関与していることを示している。
Human intestinal Bacteroides spp. RHEIN-I and RHEIN-II capable of transforming rhein to rheinanthrone, induce rhein-dependent diarrhea in rats
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