Formation of 20 beta-dihydrosteroids by anaerobic bacteria.

Cortisol was metabolized to a variety of products, among them small amounts of cortol by fecal flora of humans and rats. A microorganism, Bifidobacterium adolescentis, isolated from both sources, synthesized a 20-hydroxysteroid dehydrogenase which reduced cortisol to 20 beta-dihydrocortisol. The metabolite was reduced to cortol by Clostridium paraputrificum. The 20-hydroxysteroid dehydrogenase showed a wide substrate specificity; it was independent of the 4-ene and the configuration at C3, C-11, C-17 and C-21. Cortol was resistant to any further alteration by human fecal flora, i.e. it is a metabolic end product. As expected, B. adolescentis effectively prevented 21-dehydroxylation of cortisol by Eubacterium lentum.