Strains of bacteria characterized by exhibiting: (a) a
7.alpha.-dehydroxylase activity of less than 50%, and (b) bile acid
deconjugation activity of less than 50%, and descendants, mutants and
derivatives thereof preserving activities (a) and (b); and a
pharmaceutical composition using one or more of such strains and use of
same for preventing and treating diseases associated with or caused by an
altered metabolism of bile acids.