ABSTRACT
The human gastrointestinal tract harbors a complex collection of microorganisms, which
form a specific individual microbiota for each person. This specific microbiota is depen-
dent on the environment and genetic factors. The total number of microbes in the intestinal
tract can be estimated at 1012 bacteria/g of intestinal contents. Several hundred bacterial species can be identified using traditional culture methods. The use of molecular methods
has increased the number of bacteria in the intestinal mucosa and intestinal contents and
also changed our understanding of the composition of the intestinal microbiota. The
microbiota is metabolically active, and its composition is related to many disease states
within and outside the intestine.