Degradation of quercetin-3-glucoside in gnotobiotic rats associated with human intestinal bacteria

Aim: The two bacterial species, Eubacterium ramulus and Enterococcus cassel iflavus, which had previously been isolated from human faeces using the fla vonoid quercetin3-glucoside as the growth substrate, were tested for their ability to utilize this compound in vivo. Methods and Results: Germ-free rats were associated with Eu. ramulus and su bsequently with Ent. casseliflavus and vice versa. Identification and enume ration of the bacterial cell counts in faeces and intestinal contents were performed by whole cell fluorescence in situ hybridization. Eubacterium ram ulus and Ent. casseliflavus occurred in caecal and colonic contents at cell counts of up to 10(10) g(-1) dry weight. In the jejunum, only Ent. casseli flavus was found (10(9) g(-1) dry weight). Upon oral administration of 32 m u mol quercetin3-glucoside, quercetin was detected in the faeces and urine of germ-free rats (2.2 x 10(-1)-8.1 x IO-I mu mol 24-h(-1) faeces collectio n and 1.0 x 10(-2)-2.8 x 10(-1)mu mol 24-h(-1) urine collection, respective ly) and of rats monoassociated with Ent. casseliflavus (7.9 x 10(-1)-2.7 mu mol 24-h(-1) faeces and 1.0 x 10(-1)-5.9 x 10(-1) mu mol 24-h(-1) urine, r espectively). In contrast, the faeces and urine of rats associated with Eu. ramulus contained 3,4-dihydroxyphenylacetic acid (4.7 x 10(-2)-3. 6 mu mol 24-h(-1) faeces and 2.4 x 10(-2)-1.0 mu mol 24-h(-1) urine, respectively) but only low, or undetectable, concentrations of faecal quercetin (up to 9. 3 x 10(-2) mu mol 24-h(-1) faeces; detection limit 2.5 x 10(-2) mu mol). Ur inary quercetin concentrations varied markedly from undetectable amounts up to 1.0 mu mol 24-h(-1) urine (detection limit 1.0 x 10(-2) mu mol). Isorha mnetin was found in the urine of all animals independent of their bacterial status. There were no significant differences between the groups (2.0 x 10 (-2)-2.8 x 10(-1) mu mol 24-h(-1) urine). In complete intestinal tissues of animals, associated with. both species, quercetin-3-glucoside and its meta bolites were detected by a more sensitive and selective method at concentra tions that were two to three orders of magnitude lower than in faeces or-ur ine. Conclusions: These results indicate that Eu. ramulus may be a key organism for the bacterial transformation of flavonoids in the gut.