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My name is Dr. Nita Salzman.
I am a Professor of Pediatrics
in the Division of Gastroenterology
at The Medical College
of Wisconsin.
The title of my presentation today
is "Paneth Cells,
Antimicrobial Peptides,
and the Regulation
of the Intestinal Microbiota".
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Humans and other mammals
are colonized
by a vast number
of diverse microorganisms
collectively known
as the microbiome.
The human microbiome is defined as,
"The totality of microorganisms
and their collective
genetic material
present in
or on the human body."
The human microbiome,
while predominantly bacterial,
is also comprised of viruses,
archaea, and eukaryotic microbes.
Each body site harbors
a distinct microbiome.
The GI tract is the largest
mammalian mucosal surface
and contains the majority
of the total human microbiome.
The majority
of the bacteria comprising
the microbiota resist culturing
by conventional techniques.
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The GI tract is the largest
mammalian mucosal surface.
And this mucosal surface
is highly colonized
by a diverse microbial ecosystem.
If you consider the GI tract
as a tube
that starts at the mouth
and ends at the rectum,
the red dots depicted
in this cartoon
represent bacterial colonization.
Mammals including humans
are colonized
by vast numbers of microbes,
predominantly bacteria.
And the majority
of these colonizers
are in the GI tract.
At current estimates
between 500 and 1,000
different bacterial species
can be found in the GI tract.
Anaerobic bacteria outnumber
aerobic bacteria by 10-100 fold.
Bacteria in the GI tract
are comprised
of transient organisms
and indigenous organisms.
And currently,
there is no accepted way
of distinguishing these groups.
The overall dominant phyla
in the small and large bowel
include the Bacteroides
which are Gram-negative,
and the Firmicutes,
which are Gram-positive.
The most abundant members
of the Firmicutes phylum
are clostridial species.
The density of colonization
as well as the specific composition
and diversity of colonization
is dependant on site
and specific
intestinal microenvironment,
including pH, oxygen environment,
nutrient environment,
and likely several factors
that are yet undetermined.
The mouth,
which is generally at a neutral pH,
is highly colonized.
The esophagus has a low level
of resident microbiota.
While the stomach has somewhat
increased bacterial abundance.
The proximal small intestine
reflects the bacterial burden
of the stomach,
at about 10 to the 4th cfu/ml.
But the bacterial burden increases,
as you move distally,
ultimately reaching 10 to the 8th
cfu/ml in the terminal ileum.
At the junction,
between the terminal ileum
and the large intestine,
there is an abrupt change
in bacterial abundance,
with the highest abundance
of bacteria
in the large colon at approximately
10 to the 12th cfu/ml.
Although the bacterial composition
are similar at the phylum level,
there are significant differences
between the small
and large intestine,
with respect
to both bacterial diversity
and relative abundance
of specific bacterial taxa.
