The present invention relates to methods and compositions for reducing the risk and severity of vancomycin-resistant Enterococci infection or colonization. It is based, at least in part, on the discovery that a restricted fraction of the gut microbiota, including the bacteria Clostridium scindens and/or the bacteria Blautia producta contribute substantially to resistance against vancomycin-resistant Enterococci infection or colonization. Without being bound by any particular theory, it is believed that this is achieved through the biosynthesis of secondary bile acids in the case of Clostridium scindens.

The invention relates to novel biocatalytic processes comprising the whole cell reduction of dehydrocholic acid (DHCA) compounds, novel 7-hydroxy steroid dehydrogenase mutants, the sequences coding for these enzyme mutants, methods for producing the enzyme mutants and use thereof in enzymatic conversions of cholic acid compounds, and in particular in the production of ursodesoxycholic acid (UDCA); also a subject of the invention are novel methods for the synthesis of UDCA using the enzyme mutants; and in particular a further improved method for producing UDCA using recombinant whole cell biocatalysts.

The invention relates to novel 7-hydroxysteroid dehydrogenase mutants, to the sequences which encode these enzyme mutants, to processes for the preparation of the enzyme mutants and to their use in enzymatic reactions of cholic acid compounds, in particular in the preparation of ursodeoxycholic acid (UDCS). The invention also relates to novel processes for the synthesis of UDCS using the enzyme mutants; and to the preparation of UDCS using recombinant, multiply-modified microorganisms.

In various aspects and embodiments, the invention provides a nucleic acid molecule comprising a nucleotide sequence encoding a 7-hydroxysteroid dehydrogenase (7-HSDH) mutant that catalyzes at least the stereospecific enzymatic reduction of a 7-ketosteroid to the corresponding 7-hydroxysteroid, wherein the mutant has, compared to the wildtype 7-HSDH of SEQ ID NO:2, a decreased substrate inhibition and/or an altered cofactor usage, and the mutant has, in comparison with the wildtype 7-HSDH of SEQ ID NO:2, 1 to 15 amino acid additions, substitutions, deletions and/or inversions in the sequence motif VMVGRRE corresponding to positions 36 to 42 of SEQ ID NO:2.