You are not just a person – you are an ecosystem. Your body
is home to trillions of microscopic
critters, including viruses, bacteria, and fungi, living on or inside you.
Collectively, these communities of microbes constitute what is called your
“microbiome”.
And there are more of “them” than “you” – the number of
microbes inhabiting your body is larger than the number of cells making up your
body! To put this in perspective, it has been estimated that your microbiome
weighs about 3 pounds. Good news if you’re on a diet – when you step on the
scale tonight, feel free to subtract 3 pounds of stuff that isn’t “you” per se.
A new study concerning our microbiome seems to be coming out
each week, so it is time we get to know our microbial roommates.
1. Where does your microbiome come from?
We are born virtually sterile, but quickly receive an infusion
of bacteria from our mom, first through the birth canal and then through the milk.
Over 900 species of bacteria have been found in breast milk, and these are the
pioneers that settle into your gut, which appears to stabilize by the age of 3.
Of potential interest are babies born by caesarean section or those who are fed
formula instead of breast milk. Babies delivered via C-section do in fact have
a different microbiome and may be at higher risk for certain types of allergies
and obesity (more on this below). Our microbiome continues to receive fresh new
imports as we move through, inhale, and ingest our environment.
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| How much of you is really you? There are more microbes in your body than the number of cells making up your body. We are just now beginning to appreciate the many things they do for us. |
2. Your microbiome is like your own personal “germ cloud”.
You’ve probably noticed that everyone’s home smells a little
different. Sometimes this is due to cooking, pets, or the amount of trash they
let accumulate, but it is also due in part to the microbiome of the inhabitants.
Researchers have found that you are surrounded by a “germ cloud”, and you leave
pieces of your microbiome wherever you go like a trail of breadcrumbs. It might
even be possible for police to use microbiomes to track people one day like
they currently use fingerprints or DNA. In other words, you have a “microbiome
fingerprint” that is left behind like a germ echo wherever you go.
This “germ cloud” may also explain how dogs can track people
so easily. The byproducts generated by the millions of bacteria living on your
skin are aromatic (odorous), producing a scent that is released into the air as
you move. Animals with a keen sense of smell can get a whiff of these aromatic
compounds and follow them to the source.
Speaking of “germ clouds”, if you ever wondered if it is
possible to fart out germs, some brave scientists have sniffed out the answer
to this question. You can read about the results here.
3. Antibiotics substantially alter your microbiome.
We take antibiotics to get rid of pathogenic bacteria that
make us sick. The problem is they are not selective, so they destroy a lot of
our friendly bacteria in addition to the bad guy. We need these friendly
bacteria to do all sorts of things – to name just a few: they help us digest food, make vitamins, and build
anti-inflammatory compounds.
Another important thing our microbial friends do is keep
infections in check. For example, yeast infections from pathogenic fungi can
arise if good bacteria are not around competing for resources. And some
bacteria, like the nasty Clostridium
difficile, are naturally resistant to many antibiotics. When good bacteria
are killed as collateral damage in an antibiotic treatment, the growth of Clostridium can run amok. These bacteria
secrete a toxin that causes diarrhea and they can lead to a life-threatening
superinfection in some patients.
4. Your microbiome may protect you from allergies or obesity.
Dr. Martin Blaser has found that administration of
penicillin to mice soon after birth altered their gut microbiome in such a way
that it made
them more prone to obesity as adults. Remarkably, the tendency to grow
obese is transferrable to germ-free mice – in other words, by transplanting the
microbes from the penicillin treated mice to normal mice made the normal mice
more susceptible to weight gain.
Studies such as these make it tantalizing to speculate that
we may be able to treat certain ailments in humans by altering our microbiome
with specific probiotic regimens. Maybe they could even slip these bacteria
into our peanut
butter instead of deadly Salmonella.
5. How do scientists study the microbiome?
Advances in DNA sequencing have allowed scientists to
rapidly map the genomes for many microbial species, which provides us with a
“genomic fingerprint”. We can process samples swabbed from the skin or body
cavities, or process stool samples, for DNA sequencing. Usually just sequencing
the 16S ribosomal RNA gene is enough to distinguish one bacteria species from
another.
It should be mentioned that some scientists are issuing cautions
about over-interpreting microbiome studies. Many of the studies altering
the microbiome have been performed in mice, so it remains to be determined to
what extent the findings can be extrapolated to humans. Furthermore, many of
the methods used to alter the microbiome in lab animals do not faithfully mimic
what humans do with antibiotics. For example, in some studies the investigators
give large doses of antibiotics over unusually long periods of time to see an
effect in lab animals, which does not equate to the typical dosing of
antibiotics in humans. Finally, many of these studies are correlative and have
not yet definitively demonstrated causation. There is a big difference
between correlation and causation.
6. So should I take my microbiome into my own hands?
Much more research needs to be done to assess the true
impact of the microbiome versus other factors that come into play, such as host
genetics, diet, and the environment. It is argued that some microbiome studies
are hyped up and way
overblown. Long story short: if you
or your child becomes sick with an infectious agent, it is not wise to withhold
antibiotic treatment out of fear that it will cause allergies or obesity. If
you are overweight, a healthier diet and plenty of exercise is going to do much
more than any probiotic pill. In fact, there is little evidence that the
popular probiotics on the market do anything to remedy the wide-ranging health
problems some claim to treat, although there is data
showing potential benefit in treating some gastrointestinal maladies,
especially acute diarrhea caused by rotavirus.
Go here
to learn more about the NIH human microbiome project.
Contributed by: Bill
Sullivan, Ph.D.
Follow Bill on
Twitter.
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