Hand sanitizer sales in the US total about $180 million a year. Add to that all the Lysol, bleach, and other cleaners we use to eradicate harmful germs and we’re talking about a hefty sum indeed. Then there’s the copious amount of antibiotics we pop at the first sign of infection. The average child in the US receives approximately one course of antibiotics each year. Of course, these drugs have saved countless lives, but their use—along with but to a lesser extent the use of things like hand sanitizers and antibacterial soaps—comes with collateral damage. Only now are we beginning to understand the extent of that damage.
Let’s back up for a moment… way back to the late 17th century. It was then that Dutch scientist Anton van Leeuwenhoek decided to scrape his teeth and place the sample under one of his handmade microscopes. According to Leeuwenhoek: “I found, to my great surprise, that it contained many small animalcules, the motions of which were very pleasing to behold.”
What Leeuwenhoek glimpsed for the first time was part of what is now collectively known as the human microbiome. Consider this staggering statistic: our bodies are comprised of ten times more microbial cells than our own human cells. What’s more, in terms of genes, there are approximately 100 times more bacterial genes playing a role in your life than there are human genes. As biologist Bonnie Bassler likes to say, “At best you’re 10% human, more likely about 1% human, depending on which of these metrics you like. I know you think of yourself as human beings, but I think of you as 90% or 99% bacterial.”
This microbiome, which consists primarily of bacteria but also some viruses and fungi, is a set of microbial communities that co-evolved with us and we with them. It has become part of the natural human landscape. “It is an extension of self,” says microbiologist David Relman. Its importance to our health cannot be overstated.
We get our first dose of bacteria as we pass through the birth canal. Then we’re introduced to more through our mother’s milk, and so on as we’re held and kissed and then as we eat and play when we start to get a little older. Eventually, our microbiome grows to include perhaps over 10,000 unique species of bacteria. And while the majority live in our gut, they also reside on our skin, in our mouths, and inside our respiratory tracts.
From early on these bacteria protect us. They fight off bad bacteria and somehow help teach our immune system the difference between good and bad. They also help feed us, producing vitamins like B3, B6, B12, and K, and allowing us to take advantage of the complex polysaccharides of plants, which we don’t manage well on our own.
But it doesn’t stop there.
We’re starting to learn that some of these microbes may have co-evolved with us to play fundamental roles in normal brain development and function. Recent studies using mice (which are raised completely germ-free and then colonized with whichever microbes are of interest) have shown that some of these bugs play a role in regulating things like anxiety, learning, and appetite, among other complex behaviors.
One mechanism by which bacteria in your gut can affect your brain is via the vagus nerve, which contacts the gut lining and extends all the way up to the brainstem. A study at Caltech showed that this is the mechanism by which a bacterium called Lactobacillus rhamnosus is able to affect depressive-like behavior in mice. Mice that were treated with this bug exhibited less depression-like symptoms than the germ-free mice.
Another mechanism by which bacteria can affect the brain is by activating the immune system, since approximately 80% of our immune cells live in our gut. Interestingly, immune abnormalities contribute to several neurological disorders. In another study at Caltech, scientists showed that this is how the bacterium Bacteroides fragilis helps prevent a mouse version of multiple sclerosis.
That same bacterium, Bacteroides fragilis, was shown in a separate study at Caltech to be able to correct what scientists called “the communication deficit” that is a hallmark symptom of autism by activating the gut endocrine system. In this study, mice that were classified as autistic-like and displayed less than normal communication became “normal” when treated with the bug.
Obviously this science is still very early stage, and no one knows if it could ever work in humans, but the implications of these studies is still profound. They suggest that microbe-based therapeutics could one day help treat a host neurological disorders. That’s mind boggling.
So maybe we should think twice about the war on bacteria before we kill off the very bugs that help us survive and live a healthy life. Unfortunately, some damage has already been done. Scientists have already found that the microbial diversity in the guts and on the skins of the Yanomami, a group of hunter-gatherers who live in the Amazon rainforest, is twice that of an American city-dweller. Furthermore, researchers studying how antibiotics alter the gut microbiome say their findings link use of the drugs early in life with obesity and other metabolic conditions later on.
There’s even more to the story when it comes to some of the “bad” bugs. In 1982 Barry Marshall and J. Robin Warren shocked the medical world when they discovered that the bacterium Helicobacter pylori (H. pylori) is the principal cause of gastritis and peptic ulcers. Doctors could now effectively treat ulcers with antibiotics. Scientists the world over began calling for the total destruction of H. pylori. As one prominent gastroenterologist wrote in 1997, “The only good Helicobacter pylori is a dead Helicobacter pylori.” The problem is, it was later discovered, is that while H. pylori does indeed cause problems later in life for some people, it performs beneficial functions early on, beginning in infancy. In fact, studies have shown that without H. pylori in our guts, we may be at greater risk of developing asthma or becoming obese.
Again, a lot of this science is still early stage; but one thing has become clear: to truly understand ourselves and our health, we need to understand our microbiomes.
Not all bacteria are good, of course. A number of these little microorganisms are problematic, some even life-threatening. But the technology developed by this month’s recommendation in Casey Extraordinary Technology promises to make short work of the most menacing strains of bacteria—including so-called superbugs like MRSA. Also joining the fight in the near future will be our ability to create antibiotic “smart bombs” by exploiting what’s known as CRISPRs—a topic that’s explored in the feature article of the most recent CET. To gain immediate access to this issue and all our past publications, simply sign up for a 90-day risk-free trial of Casey Extraordinary Technology.