Despite its efficacy, the mechanisms of FMT are poorly understood,
though the concept behind the procedure seems intuitively
straightforward.
Even the earliest investigators using FMT in the
1950s
recognized the importance of gut microbiota in the normal
function of the gastrointestinal tract, and made a connection
between
the use of antibiotics and the clinical syndrome caused by
the
infection [5]. They hypothesized that restoration of the normal
microbial
gut ecology by transfer of entire microbial communities
from healthy donors could be curative in this disease. Recent
experiments
have largely validated this hypothesis, although it
remains
unclear
how
these transferred microbiota are able to combat
the infection. Potential mechanisms include competition for
limiting
resources
by other microorganisms within the same ecological
niche in the intestinal tract, direct elimination of C. difficile or
interference
with
its pathogenicity by microbial products, restoration
of secondary bile acid metabolism in the colon, and induction
of immune-mediated colonization resistance. These various mechanisms
were reviewed recently in several articles [31,32], and
this review will focus primarily on immune-mediated colonization
resistance.