Have you ever wondered what it means to be human? Well, it turns out that only a tiny percentage of what you and I are made of is in fact human. And we need these non-human bits to survive. But we're doing dreadful things to this hidden majority, and it's damaging our health in ways that we are only just discovering.
It is said that we are 10 parts microbe and one part human. And that's counting microbial cells as the unit. If we count unique genes, then the difference is a factor of 100. We are only 1% human in terms of unique genes. So you and I are mostly bacteria of some kind. We need each other to stay healthy.
And there's now a name for this part of ourselves. The human microbiome is a set of microbial communities that have co-evolved with us and we with them and have become part of the human landscape. It is an extension of self.
They provide to us untold functions that we Don't have the means of executing. We're born deficient in our ability to digest certain kinds of foodstuffs. For example, the complex polysaccharides of plants. We can't manage those very well. Our microbes provide us the means of taking advantage.
They also help us manage lots of other encounters with the environment. One of the things our microbiome does is give us an internal shield of friendly microbes which protect us against invasion by some of the nasties out there. The good guys try to crowd out the bad ones.
It's competitive exclusion. Another term for it is colonization resistance. So, you know, they man the beachhead and make it hard for others to arrive and find space.
So where are these microbes? Well, while most are in our bowel, They can in fact be anywhere where we're exposed to the outside world. So we have them in our mouth. In the mouth it's a measly 10 million per gram.
But it's only measly because in the colon we're talking about 100,000 times as many per gram. So the microbes in our bowel, for example, help us to recirculate valuable nutrients and in fact assist us to keep our cholesterol down. So we need them and they need us.
But we do some terrible things to our microbiome, like assault it with antibiotics. Yeah, unfortunately, for us and for them, everything I'm going to tell you about the untoward effects of antibiotics has to be balanced against the obvious important benefits. But I think for too long we have felt as though you can't do much wrong with an antibiotic.
So if in doubt, pull it out. And that clearly is not a good position to be taking. We've been asking volunteers to take an antibiotic, even though they didn't really need it.
We do it for... short periods of time. We watch them before, we watch them after, and we're now doing second exposures a half year later.
And the bottom line is, maybe not surprisingly, far more members of the microbial communities of the human body experience a severe impact. They're decimated many more than we thought. Now, in healthy people who might only have an occasional course of antibiotics, the microbiome seems to require a lot of work.
recover quite well. That's not so true in people who are sick and weakened. As a side effect of antibiotics, they can become infected with a germ called Clostridium difficile, which causes hundreds of thousands of deaths worldwide. So you're right, Clostridium difficile is the cause of large numbers of deaths, but even larger numbers of illnesses where there is a recovery, but after some cost.
One solution that some people suggest for this devastation to our microbiome is probiotics, substances which put back the friendly bacteria. The evidence on probiotics is... Still early to interpret, but I would say it's suggestive that there is some potential benefit there. As I said before, these friendly bugs, our microbiome, does a lot more than protect us against nasty infections.
They keep our cholesterol down and detoxify poisons. So the question is, if we damage our microbiome with antibiotic overuse, are we causing heart disease and cancer? The short answer is we don't know, because no one has looked for this particular link in the story. We simply don't know. So while in the past we've seen bacteria as the enemy and got excited about how we can kill off disease-causing germs with antibiotics, it's time for a new way of thinking.
Remember, we're talking about 99% of what we are.