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In a survey of intestinal bacteria capable of metabolizing glycyrrhizin (GL), Ruminococcus sp. PO1-3 and Clostridium innocuum ES24-06 were isolated from human feces. The former strain had the ability to hydrolyze GL to glycyrrhetic acid (GA) and to reduce 3-dehydroglycyrrhetic acid (DGA) to GA while the latter strain had the ability to reduce DGA to 3-epiglycyrrhetic acid (EGA). A mixture of the two strains could not only reduce DGA to both GA and EGA, but also epimerize GA to EGA and vice versa, possibly through a 3-dehydro intermediate.