Bengt E. Gustafsson memorial lecture. Function of the normal human microflora.

The normal human microflora maintains a delicate balance between its constituent parts, numbering 10(11) bacteria per gram with over 400 different species. Certain metabolic functions and enzyme activities can be attributed to the microflora, and these play a role in metabolizing nutrients, vitamins, drugs, endogenous hormones and carcinogens. Our laboratory has studied estrogen and cholesterol metabolism and activation of colon carcinogens. Three techniques to change the flora and its enzymatic activities have been used. Switching the diet from an omnivore diet to a vegetarian diet decreases bacterial deconjugating enzymes in the intestine. Administering antibiotics also suppresses the metabolic activity of the microflora. Similar suppressive effects can be achieved by feeding a human strain of Lactobacillus that implants in the gastrointestinal tract. Manipulation of these various modalities can maximize the beneficial activities of the intestinal microflora.