ABSTRACT
The potential for metabolism of a substrate by the gut bacterial flora is determined by the composition of the flora at the relevant site in the gut, the induction or production of the relevant enzymes, and the activity of those enzymes. In studying the factors affecting bacterial metabolism most workers have used animals and so there are difficulties in interpreting the results to increase our understanding of the human. Bacterial bile acid 7α-dehydroxylase has a pH-optimum close to neutral and the activity decreases sharply with increasing acidity or alkalinity. Bacterial N-nitrosation in the urinary bladder is very much greater in mixed infections than in infections due to a single organism and this is probably due to the production of co-factors. A major factor in determining the composition of the flora ought to be the ability to resist host factors but this has been difficult to demonstrate.
