Meet Your Microbes

You.  Yeah YOU.  Guess what?  You are positively crawling with microbes.  Bacteria, viruses, fungi, and protozoa.   An average-sized human is host to approximately 38 trillion microbes, which is slightly more than the number of actual cells in the human body.  The vast majority of them, up to 90%, reside in your gut.  Microbes are on every patch of your skin.  They’re on your eyeballs. In your ears.  In your lungs.  Wait!   Before you reach for the soap, consider what science has to say about your own personal microbiome.  The field of Microbiome Science is a new one, just 15 years old, but its findings reveal that the bugs you are carrying around are not usually pests or invaders.  They are symbiotes living in harmony with you, and they just might play a bigger role than you think in making you who you are.

Oral bacteria. Colored scanning electron micrograph (SEM) of mixed oral bacteria. The mouth contains a large number of bacteria, most of which are harmless or even beneficial. However, some bacteria can cause throat infections or cause the formation of plaque deposits on the teeth, which may lead to decay. Magnification: x10000 at 10cm wide.

In (and on) your body there is an entire ecosystem that you will never see.  According to scientist Richard Losick, there are thousands of different species of bacteria in the human body.  It appears that our own microbiomes are completely unique, too – it’s possible for two people to have absolutely no overlap in the microbes that inhabit their body.  There is evidence that our personal microbiomes have a surprising level of influence over us – from how much we eat, to how well we perform athletically, to perhaps even influencing our moods.  The new field of Microbiome Science has only begun and so far studies are small, usually involving studying stool samples from humans and then transplanting them into mice to study the effects.  If the idea of a fecal transplant turns your stomach, it might help to know that ingesting another person’s gut microbiome has been a proven therapy in humans to cure a severe antibiotic-resistant intestinal infection known as Clostridium Dificile.

Getting to know the world of microbes has occupied scientists ever since microbes were discovered, and there’s so much more to discover. This is a 19th century artist’s vision of “France in the Year 2000.” Jean Marc Cote(?), Public domain, via Wikimedia Commons

How much influence do microbes really have over us?  And how do they do it? Gut microbiota have been the best studied so far.  It appears that different kinds of intestinal flora can release different kinds of chemical signals that, via nerve cells, immune cells, or the bloodstream, can signal directly to the brain.  For example, we get our sensation of fullness after a meal from our hypothalamus region in the brain.  The hypothalamus gets its signal from chemicals released by enteroendocrine cells in the intestinal wall.  But the enteroendocrine cells themselves are triggered by chemical signals from gut bacteria.  If there is an overgrowth of dangerous bacteria in the gut, other bacteria can send chemical signals to the dendritic cells of the immune system, beginning an immune response.  Some evidence even indicates that certain gut microbes can trigger enterochromaffin cells, the cells that contain the “happy chemical” serotonin.

Although pretty, these Streptococcus Pyogenes bacteria would probably elicit an immune-signaling response from your microbiome.

Can the tiny hitchhikers in your gut really influence mood and overall quality of life?  At the University of Turku in Finland, Dr. Anna Katariina Aatsinki and her colleagues took stool samples from 301 babies.  Babies with the highest proportion of Bifidobacterium were also most likely to exhibit a trait the researchers called “positive emotionality,” a.k.a, happy babies.  In one of the more extensive studies, researchers at Harvard took samples from marathon runners before and after they ran Boston Marathon, and compared them with samples from non-runners.  The marathon runners had a much higher proportion of a bacteria called Veilonella Atypica, which was quite an interesting discovery for the researchers.  Veilonella is a microbe that metabolizes lactate, the same kind of lactate that is produced by muscles as a byproduct of a vigorous workout.  In turn, Veilonella releases propionate, which helps with oxygen metabolism and heart rate.  When mice received a transplant of the runners’ stool, and were given tiny treadmills to run on, the mice who received it ran 13% percent longer than the control group! 

These Eubacteria from yogurt are the friends you want in your microbiome!

Microbiome science is a growing field with tantalizing promise. Could the detectives of the future take “microbiome prints” to identify a suspect?  Could there be a future in which a dose of the right probiotics change a person’s life?  Science is indicating that even though our microbes are tiny, our microbiome is MIGHTY!

A true story of a fecal transplant, discussed by a doctor and patient at the Mayo Clinic:

Dr. Richard Losick on Human Microbiome Research:

The Microbe Menagerie (Paywall):

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