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Marta Gysel Reviewer: Ariana Bleau Lugo ﻿So you think you are human. There's 7 billion people on this planet. You know how many microbes there are? 5 nonillion. That's the number of stars in the universe multiplied by 5 million. That's a lot of bacteria. And they are everywhere. They are on this floor, they are in your kitchen sink, they are on your chair, they are on your coffee cup.
00:44
And yes, they are on you. You harbour 100 trillion bacteria in and on your body right now. That's only a thousand times the number of individuals on this planet, and if you look at it in terms of cells, you are outnumbered ten to one. You are not human. You are a walking bacterial colony. (Laughter) We have several commensal floras, or commensal microbiotas, as we call them.
01:26
You have your skin flora, your oral flora, your genital flora, and most famously, your gut flora. And these floras are numerous, but they are good for you. They help you digest your food, they protect you against patogens, they provide you with essential nutrients such as vitamins, they train your immune system and most importantly, if something goes wrong with your flora, something is wrong with you.
01:58
So we scientists, in the last few years, we've discovered new techniques to study the gut flora or the gut microbiome at great resolution. So we start off from a sample from your flora, we extract all the microbes, we extract all the DNA from these microbes, we throw that into one of those sequencing devices and we learn something about that ecosystem, because it's an ecosystem.
02:24
We learn what microbes live there and we learn what these microbes can do, what genes they have in their collective genome. And we've learned that our microbiome, so the collective genome, contains 100 times more genes than we have. We have a second genome active in and on our bodies. And we've learned that you can sort of classify the gut flora into 3 kinds, 3 corners of ecosystem space, and we've called them enterotypes.
03:01
And so to give you a better feeling of what these enterotypes are I often make the -- -- what's the word? -- the comparison, thank you, with an ecosystem, right, with a forest. You have tropical forest, you have temperate forest, you have bamboo forest. They are all forests. But you have different species living together and functioning as a unit.
03:30
You have constellations that work optimally, and that's what I think these constellations in your gut flora are like. And so the environment that these bacteria live in, they determine these constellations, it seems. And the environment in the gut is the food that you eat. And so people have discovered that the people that have more fat in their food, or more protein in their food or more carbohydrate in their food, they have different gut compositions.
04:01
And that's important, because more and more diseases are linked to disturbances of your gut flora. Diarrhea, diabetes, obesity, atherosclerosis, colitis, Crohn's disease, even autism, all have been associated with disturbed gut floras. And it's not merely associations. Bad gut floras can actually cause disease.
04:30
If you take the flora of an obese mouse and you put it into a germ free mouse, so one that doesn't have a flora, that germ free mouse becomes obese. So we are thinking, right, we can learn something from this flora about your personal health. We are moving towards diagnosing people on the contents of your gut.
04:55
And so this is being done, for example, for diabetes, or for colon cancer. But we can do this in everyday life. We can go towards lifelong health monitoring of your gut flora from the obvious material. And when I mean lifelong, I mean lifelong, because your gut flora is seeded at birth. Babies are born sterile and it's only when they get born that they are inoculated by the flora of the mother: the skin flora, the vaginal flora, the fecal flora.
05:34
That's when it happens, that moment. And so messing with the flora in early life can have serious consequences, and we are starting to understand more and more how serious these consequences can be. Babies that are born by C-section have different floras than babies that are born vaginally. Babies that have been breastfed have different floras than babies that have been formula-fed.
06:03
We don't really know which one is better, we just see the differences at the moment. But we know that babies or, for example, again, from mouse experiments, mice that have had low dosage of antibiotics at a very early age have a disturbed flora at adulthood and they become obese. And low dosages of antibiotics at early age have been linked to things like asthma.
06:33
So we have to start thinking and be very careful about the usage of antibiotics. I'm not pleading against the antibiotics, but we should be very careful. Also in adults this matters. If you get a normal dose of broad spectrum antibiotics, some of you will recover after a few weeks. The gut flora will recover after a few weeks.
06:56
For some of you it will take months. For some of you it can take over a year for your gut flora to become normal, or what it was, again. And some of the people, they never recover. They have permanently altered their gut flora. Again, there's so many unknowns in our field. We don't really know what the effects of this are.
07:17
But we are just seeing that the consequences are important. As well as we can also think of modulating your flora, resetting your flora. There's now a new thing, called fecal -- it's not a new thing, actually. It's pretty old, Bedouins have used it for ages. But fecal transfer, transplanting of flora of a healthy individual into a diseased individual actually seems to work as a therapy, in some diseases.
07:55
And it's not only disease. The gut flora influences behavior, influences brain development. Experiments in mice are now showing that anxiety behavior or explorative behavior of mice is determined by what flora they have. In Drosophila, the flora has been shown to be influencing mating behavior, sexual preference.
08:29
So... think about it. Or, is it you who is thinking? So, take home messages: I only have two. One is, take care of your friends. But the second one is: You never have to feel lonely ever again. (Laughter) Thank you. (Applause)
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