Comparison of plasma and cecal quercetin in <i>Enterococcus</i> sp. rutin_18 mono-associated and germ-free mice fed rutin-supplemented diet

Rutin is a functional compound with both antioxidant and anti-cancer properties. The hydrolysis of rutin glycosides by intestinal bacteria is important for rutin absorption. We isolated <i>Enterococcus</i> sp. rutin_18, an intestinal bacterium that can convert rutin to quercetin, and investigated the possibility of <i>Enterococcus</i> sp. rutin_18-mediated rutin conversion to quercetin <i>in vivo</i> using mono-associated mice. We compared the plasma and cecal quercetin levels in rutin-metabolizing <i>Enterococcus</i> sp. rutin_18 mono-associated (Entero) and germ-free (GF) mice fed a rutin-supplemented diet. The plasma quercetin, isorhamnetin, and tamarixetin concentrations were significantly higher in the Entero mice than in the GF mice. The cecal rutin concentration was significantly lower in the Entero mice than in the GF mice (p<0.001). We found that <i>Enterococcus</i> sp. rutin_18 converted rutin to quercetin in the Entero mice. We infer that the <i>Enterococcus</i> sp. rutin_18 used in this study is an important intestinal bacterium that converts rutin to quercetin.