Look in the mirror and you won't see your microbiome. But it's there with you from the day you are born. Over time, those bacteria, viruses and fungi multiply until they outnumber your own cells 10 to 1.
As babies, the microbes may teach our immune systems how to fight off bad bugs that make us sick and ignore things that aren't a threat.
We get our first dose of microbes from our mothers, both in the birth canal and in breast milk. Family members tend to have similar microbiomes.
"The mother's microbiome has actually poised itself over nine months to basically become the prime source of microbes to the infant," says Lita Proctor, director of the Human Microbiome Project at the National Institutes of Health.
But ultimately each person's microbiome seems to be unique, perhaps as personal as a fingerprint.
As the microbes colonize our bodies, they pick specialized real estate. The mouth, with all those moist nooks and crannies, is home to one of the most diverse habitats, like the Amazon jungle.
Wet places like our armpits are lush, too. But they have different microbes than those in the mouth.
The armpit microbes feast on nutrients in sweat, Proctor says, and produce antimicrobial compounds to protect the skin against harmful microbes.
Other body parts are like the Sahara Desert to your microbes. That forearm skin, for example, is dry — very dry. But even that driest habitat is brimming with microbes.
Feet have oily parts and dry parts, and it's those wet parts that the foot fungus just loves.
But the biggest habitat is the gut. It hosts the most complex and diverse group of microbes. Everything that microbes are doing elsewhere in the body, they're doing in the gut, in spades.
Diverse as these habitats are, the microbes on the various body parts communicate with each other and with our cells. Scientists have started eavesdropping on those conversations, and have started testing them as possible treatments for diseases like Crohn's, multiple sclerosis and asthma.
This research is all really new. No one knows for sure what most of our microbes are doing. But many scientists now think that if we're going to remain healthy, we have to maintain the health and well-being of the ecosystems for our microbes.
NPR has been exploring the world of the microbiome. To read and hear our series, click here.
STEVE INSKEEP, HOST:
On a Monday, it's MORNING EDITION from NPR News. I'm Steve Inskeep.
RENEE MONTAGNE, HOST:
And I'm Renee Montagne, good morning.
Today in Your Health: More on the microbes that populate the human body. We've reported on how the microbes we all carry around with us are, for the most part, more friend than foe. Scientists are discovering how these good microbes affect our health.
Today, NPR's Rob Stein takes us on a journey through the microscopic world of the body.
SELENA SIMMONS-DUFFIN, BYLINE: Step right up, everybody - all aboard.
ROB STEIN, BYLINE: We're going to take a tour, a kind of audio bus tour through the human body...
SIMMONS-DUFFIN: Welcome. Welcome.
STEIN: ...with the help of radio producer Selena Simmons-Duffin.
SIMMONS-DUFFIN: OK. Everybody, come on up.
STEIN: But before we start our journey, let's stop and think about our bodies in a different way. Not as a single human, just out in the world walking around, but instead like this...
LITA PROCTOR: We are an ecosystem.
SIMMONS-DUFFIN: That's our tour guide, everybody, Lita Proctor.
STEIN: She works over at the National Institutes of Health.
PROCTOR: That's the larger way to think about it. The whole human body is an ecosystem, with particular habitats in different parts of the body.
STEIN: Proctor will guide us on this eco-tour through all these habitats and all the bacteria, viruses, fungi and other microbes inhabiting each of them, which collectively scientists call the human microbiome.
SIMMONS-DUFFIN: OK. Everyone, time to take your seats.
PROCTOR: Let's take a tour of the human microbiome.
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SIMMONS-DUFFIN: We've arrived at the first stop on our tour, starting at the top of the body.
PROCTOR: Your mouth.
STEIN: Your mouth, with all those little nooks and crannies, is home to one of the most diverse habitats. Like the Amazon jungle, it's just teeming with organisms.
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PROCTOR: Because there's so many places they can grow: on your tongue, on your teeth, on your gums. The microbes that live in the roof of my mouth are different than microbes that are growing on the surface of my tongue.
STEIN: Some can cause gum disease but most may be helpful.
PROCTOR: These microbes produce all kinds of compounds. And when they flow through the rest of your body they seem to be closely associated to things like Type 2 diabetes or heart disease or even cancers.
STEIN: The precise mix of bacteria in the esophagus, for example, seems to play a role in whether someone develops acid reflux and perhaps, esophageal cancer.
SIMMONS-DUFFIN: All right, everyone. Back on the bus.
(SOUNDBITE OF A BANG)
SIMMONS-DUFFIN: Watch your step there.
STEIN: Now, before we move on to our next stop on our tour of the body, Proctor takes a few minutes to talk about where our microbiomes come from in the first place. Like many the things, it starts with...
PROCTOR: Our mothers.
STEIN: Like our genes, we get a lot of our microbes from our moms.
PROCTOR: The mother's microbiome has actually poised itself over nine months to basically become the prime source of microbes to the infant, then as the infant passes through the birth canal, it gets coated with all these microbes.
STEIN: These microbes may kind of seed the baby with just the right mix. Combined with bacteria in breast milk and other microbes we encounter early in life, they slowly take shape in our first few years.
SIMMONS-DUFFIN: OK. If you look just ahead, you'll see our next stop.
PROCTOR: Let's go to the nose because that's actually quite interesting.
STEIN: Bad microbes try to hide in the nose, waiting to make us sick.
PROCTOR: And so, if an outside microbe comes in, some kind of germ or pathogen, your microbes themselves act as a first line of defense by preventing the entry and/or colonization of that germ.
STEIN: Lita Proctor says, that's probably one of the most important things our microbes do - protect us from infections.
SIMMONS-DUFFIN: OK. Everyone, time to move on.
STEIN: As we continue our tour, Proctor explains that the overall mix of our microbes looks very personal. Sort of like a fingerprint or maybe a blood type.
PROCTOR: Each of us seems to have our own unique subset of microbes that live particularly on Lita versus particularly on Rob.
STEIN: My very own microbes, lucky me. But our microbes tend to resemble those of our parents and siblings, and may stay with us for much of our lives.
SIMMONS-DUFFIN: If you look over to your left you'll see we're passing the armpits.
UNIDENTIFIED GROUP: Ohh.
STEIN: Wet places like our armpits are lush, sort of like a rainforest.
PROCTOR: That sweat that we produce is full of all kinds of nutrients that microbes love and they grow on that. While they're growing on all that delicious sweat, they're also in turn producing all kinds of anti-inflammatories and antimicrobials to protect us from microbes trying to colonize our skin.
STEIN: And different places on our skin can be very different environments: oily, like our backs or like our next stop.
SIMMONS-DUFFIN: OK. Here we are on the forearm.
STEIN: Not wet. Not oily but dry - very dry.
PROCTOR: And that could be considered like the desert of your skin microbiome.
STEIN: But even the driest habitat is brimming, just brimming with millions of microbes.
PROCTOR: But even there, there are microbes that specifically adapt to that kind of habitat, that they thrive and grow on those parts of your body where your skin flakes quite a bit.
SIMMONS-DUFFIN: OK. Everybody, time to move on - back to the bus.
STEIN: So all these different places on our bodies are totally different - but not totally independent. They're connected. And they communicate.
PROCTOR: I mean, there's a whole interaction that occurs between the different microbial habitats around the body.
STEIN: They send signals to our cells. Scientists have started eavesdropping on this complicated conversation. They've even isolated some of these signals and started testing them as treatments for diseases. Diseases like Crohn's, multiple sclerosis and asthma.
SIMMONS-DUFFIN: Everybody get ready. This is the main attraction of our tour.
STEIN: This brings us to the biggest, most important habitat.
(SOUNDBITE OF BUS STOPPING)
SIMMONS-DUFFIN: Now arriving at the gut.
STEIN: The gut. It's the nerve center - a kind of mission control.
UNIDENTIFIED MAN: Dynamic phase. Come back again with wrist code dynamics.
PROCTOR: I mean it is like the government of a country; it is like mission control.
STEIN: It's the most complex and the most diverse. And everything microbes are doing on all over the body - fighting off infections, revving up and dampening down our immune systems...
PROCTOR: That's all happening in the gut in spades.
UNIDENTIFIED MAN: Fight EDL, we've got some tweeto warnings.
STEIN: It's sort of like the command centers of our bodies.
PROCTOR: If it's not functioning properly because of genetics or poor diet or some combination thereof, that can actually lead to all kinds of diseases.
STEIN: Diseases like colon cancer, colitis, maybe even diabetes and obesity.
PROCTOR: There's apparently a role for the microbiome in the way diet is metabolized and how fat is deposited and all those kinds of things. So there's a close link with obesity and changes in the microbiome.
STEIN: Obese people appear to have less diverse gut microbiomes than lean people. Farmers fatten up their livestock by feeding them antibiotics and skinny mice get fat when scientists give them gut microbes from obese mice. So there may be a link between the rise in obesity and the explosive use of antibiotics, and other things we're doing to mess up our gut microbes.
PROCTOR: In this modern society, we are just not exposed to as many microbes as we have in the past.
STEIN: Our microbial habitats look like they're much less diverse than earlier generations, and people in less developed countries. This may help explain why the rates of asthma and allergies have been soaring.
PROCTOR: We're not fully educating our immune system because it's not being exposed to a very wide range of microbes.
STEIN: Not being exposed because of so many C-sections, and not enough breast feeding, plus all the antibiotics kids get these days, and our obsession with cleanliness.
SIMMONS-DUFFIN: Antibacterial wipe anybody?
STEIN: So researchers are starting to identify which microbes we could take, you know, probiotics and other ways to keep our microbiomes healthy.
SIMMONS-DUFFIN: Final stop here everybody.
STEIN: Our last stop on the tour of your body's microbes is a predictably...
SIMMONS-DUFFIN: The feet.
STEIN: Our feet - they've got a little bit of everything.
PROCTOR: Feet: there's oily parts, there's dry parts, there's wet parts of your feet. And all those different parts of your feet - you're just looking at your foot - you know, are all different types of habitats for microbes.
STEIN: Proctor ends our tour with a big caveat: This research is really new. No one knows what most of our microbes are really doing.
But many scientists think our microbes are an essential part of us. And to maintain our health and well-being, we have to maintain the health and well-being of the ecosystems of our microbiomes.
Rob Stein, NPR News.
MONTAGNE: Tonight on ALL THINGS CONSIDERED, we'll explore how doctors are using microbes to keep us healthy and treat us when we get sick. And for the rest of our series, go to npr.org.
(SOUNDBITE OF MUSIC)
MONTAGNE: This is MORNING EDITION from NPR News. Transcript provided by NPR, Copyright NPR.