ABSTRACT
The human gastrointestinal (GI) tract is the home of a huge microbial assemblage, the
microbiota, the vast extent of which is only now being revealed. The number of micro
organisms within the intestine greatly exceeds human cells, resulting in one of the most
diverse and dynamic microbial ecosystems. Relationships among the microbes, and
between the microbiota and the host, have a profound influence on all concerned (1,2). The
GI-tract offers various niches with nutrients, those ingested and generated by the host, and
a relatively non-hostile environment to the microbes. The microbiota play essential roles
in a wide variety of nutritional, developmental, and immunological processes and
therefore significantly contribute to the well being of the host (3-6). During the last
decade, specific bacterial isolates, termed “probiotics,” have been extensively used in an
attempt to modulate the intestinal microbiota to benefit the host. Today, there is persuasive
evidence for probiotics in prevention or treatment of a number of intestinal disorders in
humans, especially for reducing bouts of diarrhea and providing relief for lactose
intolerant individuals (7,8). In order to rationally use probiotics, prebiotics or other
functional foods as therapeutic agents, in-depth knowledge of the structure, dynamics, and
function of the bacterial populations of the GI-tract microbiota is crucial.
