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Information in this article is provided for informational purposes only. Any and all information is not intended as a substitute for the advice provided by your physician or other
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Icahn School of Medicine or any affiliated Departments of the Mount Sinai Health System, New York, New York, USA
The Human Microbiome
by Jillian Capodice, LAC
The human body is home to ten times more bacteria
than the total of our own cells. The majority of bacteria
are found in the human gastrointestinal tract but there
are also large densities on the skin, mouth, and vagina.
The human genome sequence was published in 2001
and it is a profound achievement in medicine. It also
brought to light the notion that we won't be able to truly
realize its significance without understanding the
interactions between the body and the vast number of
microbes within it (1-3).
The term "microbiome" is credited to Joshua
Lederberg. Microbiome is defined as the "ecological
community of commensal, symbiotic, and pathogenic
microorganisms that literally share our body space" (3,
4). The human microbiome project was established
after the human genome sequence. The goal of the
human microbiome project is to inventory the microbial
genes and genomes of the major body sites containing
synergistic bacteria in order to learn about the role of
the microbiome in human health and disease. The
purpose of this article is to provide a short background
on some of the roles of these omnipotent organisms.
The human gut contains the largest density of bacterial
microflora in the human body. The term microflora
encompasses mostly bacteria but in addition to bacteria,
microflora also includes archaea (microorganisms similar
to bacteria), protozoa, and viruses. To put this in
perspective, bacteria are both more numerous and
older than us. If we compare bacteria to the genus,
Homo (i.e.: the genus that is modern humans and
includes extinct species such as Homo erectus and
Neanderthal) it is estimated that the origin of bacteria is
over 3.2 billion years ago versus the origin of the genus
Homo which is thought to have originated about 2.5
million years ago respectively. This implies that
microbes have had much more time to evolve and
adapt versus modern day humans, Homo sapiens. It is
also thought that there has been a long co-evolutionary
process between humans as a host and our microbiome
(4, 5).
Before introducing the main gut microflora it is again
important to recognize the relationship between the
brain and the gut. Historically the human nervous
system and the brain in particular is characterized as the
dominant system. The brain as the mothership, gives us
the features that are uniquely human such as language
and emotional expression. However the nervous
system comprises the peripheral nervous system which
includes over 200 million nerve cells that make up the
enteric (gut) nervous system. What this means is that
the central nervous system is not as impenetrable as
previously thought. It does not act independently of the
rest of the body systems and is more like a conduit for
communication. With regard to microflora, it is now
realized that there is a brain gut axis that transmits
neuronal, endocrine, and immune system signals that is
very likely dominated by gut microflora and not the
brain (4,6).
Overview of Microflora
There are more than 200 species of microflora that
live in the human gut. This is estimated to account for
about 1kg of weight and encodes a genome that is 100
times larger than the human genome (5-7). The most
common species in the gut belong to the phyla
Bacteroidetes and Firmicutes. The most common
genera include: Bacteroides, Bifidobacterium,
Clostridium, Eucaberium, Faecalibacterium,
Peptidococcus, Peptidostreptococcus and
Ruminococcus (5, 7, 8). Lactobacillius and Escherichia
are the most studied microflora but they are less
numerous than the abovementioned organisms (8).
Human microflora colonization begins early and it is
thought that children are dominated by the main phyla
by about one year old. It is also thought that the
diversity of gut bacteria varies based on factors related
to feeding (formula- versus breast-feeding), dietary
habits, antibiotic usage, hygiene, exposure to early
infections, and geography (8).
The first evidence of the impact of diet and nutritional
factors on the diversity of gut microflora are from the
study of malnourished versus well-nourished
populations. Many dietary factors have been
hypothesized to have beneficial or harmful effects on
gut microflora. Some of these include the differences in
the consumption and amounts of animal protein, plant
fiber, sugar, and processed additives.
Researchers have compared the gut microbiome of
African and Western children and described differences
in its composition (9). In this early and important study,
it was demonstrated that there were variations in gut
bacteria composition as measured by the different
presence of various bacteria phyla. For example
Actinobacteria and Bacteroidetes were more prevalent
in African children and Firmicutes and Proteobacteria
were more prevalent in the European children in this
study. This study also demonstrated that African
children had a greater prevalence of an anti-
inflammatory short chain fatty acid (SCFA) producing
bacteria. This type of bacteria utilizes plant fibers as
energy in their biochemical anti-inflammatory cascade
(9).
The relevance of this finding is that there are a
diversity of species linked to geography and diet.
Moreover other studies have demonstrated that
presence of the short chain fatty acids results in a lower
stool pH which might be linked to better gut health.
The underlying discussion point implies that diets
containing higher amounts of dietary fiber from plant
sources may improve overall gut health (9-11). It is very
difficult to study the exact molecular mechanisms that
are influenced by the diet alone on gut microflora, the
immune system, and beyond but we are now finding
that alterations in gut bacteria may be linked to a wide
variety of human diseases such as diabetes mellitus,
cardiovascular disease, and some neurologic diseases.
Immunity and the Microbiome
In addition to the connection between the nervous
system and the gastrointestinal system, gut microflora
have a profound impact on the immune system. The
human immune system is a powerful system that
protects the body from the constant encounters with
environmental microorganisms that have the potential
Jillian Capodice, LAC is a writer and the executive editor and host of the WellJillian
website & Interview Series. She is an experienced practitioner of acupuncture and
holistic medicine and specializes in acupuncture, traditional Asian medicine, herbology,
exercise, nutrition and lifestyle medicine. She has collaborated with colleagues on
research in prostate cancer, breast cancer, chronic pain and various men's health and
urologic conditions. She is one of a few specialists practicing Integrative Urology and
provides comprehensive, patient centered care for men and women with urologic
diseases and all people who seek a holistic and multidisciplinary approach to the
prevention and treatment of complex human diseases.
Jillian has authored over 33 peer-reviewed scientific papers and book chapters. She is
currently Assistant Professor and Director of the Integrative Urology and Wellness
Program in the Department of Urology, Icahn School of Medicine, Mount Sinai Health
System, New York , New York, USA *see terms and conditions.
Reprinted with permission.
“
The human body is home to ten times more bacteria than the total of
our own cells. The majority of bacteria are found in the human
gastrointestinal tract but there are also large densities on the skin, mouth,
and vagina. The human genome sequence was published in 2001 and it is
a profound achievement in medicine. It also brought to light the notion
that we won't be able to truly realize its significance without
understanding the interactions between the body and the vast number of
microbes within it.”
. . . continued on page 53
