Let Them Eat Dirt. B. Brett Finlay

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СКАЧАТЬ second child, Jacob, was born and raised on the farm and, like his big brother, he was never the slightest bit hesitant to get dirty. He was once found playing knee-deep in a cesspool of pig waste. At fourteen months he swallowed a handful of fresh chicken droppings as Julia rushed towards him to prevent it. Her initial worry that her children were going to contract a disease from all this messiness dissipated as her kids remained healthy.

      Nowadays, with her third baby strapped on her back, she doesn’t even flinch at the sight of the two older boys doing what all farm kids do: getting very, very dirty. Every single day, they come home with dirt, poop, feathers, and who knows what else caked onto their skin and clothes. They try their best to keep their farm boots for outdoor use only, but it inevitably happens that dirty boots make it onto the living room carpet. Julia makes sure to wash their hands before they eat and they rarely miss a daily bath (the color of the bathwater is a constant reminder of why daily baths are mandatory in their house).

      Even if they play outside a lot, most children growing up in urban environments rarely ever reach the level of dirtiness that Julia’s kids experience on a daily basis. From this perspective, a farm kid (and his microbes) is very different from a city kid. We are by no means suggesting that we should all allow our kids to play with animal waste, as they could become sick from this. But farms in general provide a microbe-rich environment that has proven beneficial for the development of the immune system, and that really is akin to the way we used to live, which has been seriously altered only in the past few generations.

      The vast majority of children have something in common with Jedd and Jacob, in that they all seek out dirt and enjoy getting messy and sucking on things. Why is that? Our natural behavior in the early years of life definitely tries to maximize our exposure to microbes: babies are in direct contact with maternal skin while breastfeeding, they are constantly putting their hands, feet, and every imaginable object in their mouths. Crawlers and early walkers have their hands all over the floor, and then in their mouths. It often seems that they’re waiting for the few seconds that parents take their eyes off them to almost magically find and put the dirtiest thing they can reach in their drool-dripping mouths. It makes us wonder: Are kids instinctually drawn to microbes?

      Older kids love digging in the dirt, picking up worms, rolling on the ground, catching frogs and snakes, etc. Perhaps this is actually natural behavior designed to populate kids with even more microbes. Children rarely hesitate to lick anything or anyone. As would be expected, children also suffer more infections than adults. Their vacuum-like behavior ensures that they taste the microbial world and subsequently train their immune system to react to it accordingly. If they encounter a disease-causing microbe, also known as a pathogen, their immune system detects it, reacts to it in the form of sickness, and then tries hard to remember it so that their body can prevent it from causing disease the next time this pathogen makes a visit. When the immune system encounters a harmless microbe—and the vast majority of microbes are harmless—it detects it and, through a series of mechanisms that science does not yet fully understand, decides to ignore or tolerate it. Thus, if children’s lifestyles and behaviors dictate a limited exposure to these training events, their immune system will be partially immature and will not learn how to properly react to a pathogen or how to tolerate harmless microbes. The consequence of missing out on this early training appears to be that, later in life, the immune system may react too fiercely to these harmless microbes, which could trigger inflammatory responses in various organs of the body. This contributes to the appearance of “developed country diseases” (like asthma and obesity) that are becoming so prevalent today.

Microbes to the Rescue

      Helping develop our immune systems is only part of what microbes do for us. They are in charge of digesting most of our food, including fiber and complex proteins, and chopping them into more digestible forms. They also supply the essential vitamins B and K by synthetizing them from scratch, something our own metabolism cannot do. Without the vitamin K from microbes, for example, our blood would not coagulate.

      Good bacteria and other beneficial microbes also help us combat disease-causing microbes. Experiments in our lab have shown that infections from Salmonella, a diarrhea-causing bacterium, are far worse when antibiotics are given before the infection actually occurs. Similarly, many of us have experienced the side effects of a long bout of antibiotics: abdominal cramps and watery diarrhea. The microbes we harbor live in a balanced state that provides us with so many benefits, all in exchange for a portion of our daily calories and a warm, dark place to live with regular feeding and watering.

      But changes in our modern lifestyles are altering this balance, especially during a critical window in early life. In many developed countries, about 30 percent of babies are born by cesarean section, antibiotic usage is a lot more frequent, and most children do not suffer serious infections thanks to vaccines. Far from suggesting that any of these things should be avoided, our aim is to educate parents, as well as parents-to-be, grandparents, and caregivers, about the potentially life-changing decisions we make on a daily basis by raising children in an environment that’s much cleaner than ever before. As parents ourselves, we understand that most of us do the best we can with what we have, and it is not our intention to dictate how other people should raise their children. However, as microbiologists, we are becoming increasingly aware of the key role our resident microbes have in shaping our bodies’ development. The microbial communities of babies and young children are being altered in ways that may make them sicker later in life, by the very same practices intended to keep them healthy. Talk about a double-edged sword!

      The scientific community is just beginning to grasp this new knowledge, and the general public is just starting to hear about it in news articles of (often misinterpreted) studies. Preventing serious illnesses should always be one of our biggest concerns, but we can also do a great deal to try to distinguish between a necessary intervention, such as giving an antibiotic to fight a life-threatening bacterial infection, and an unnecessary and hyperhygienic practice, such as applying antimicrobial hand sanitizers every time a child plays outside. Not all children will or should be raised like Jedd or Jacob, but we can certainly change those unneeded aspects of our far-too-clean world.

      In our classical training as microbiologists, we studied only the microbes that cause diseases and the ways to kill them. Now we acknowledge that we have, for many years, ignored the vast majority of microbes that keep us healthy. Our research labs are changing focus, and we are beginning to think it’s time for everyone to become better hosts to our microbial guests.

BUBBLE BOY

      David Vetter was born in 1971 in Houston, Texas, with a rare genetic disorder that left him without a working immune system. Any contact with a nonsterile world would mean certain death. Because of this, he was delivered by C-section and placed in a sterile bubble immediately after his birth. In a controversial medical decision, he lived in the hospital in a bubble that grew with him. His medical treatment included many courses of antibiotics to prevent any bacterial infection. Being devoid of bacteria meant that doctors also had to feed him a special diet, along with the essential vitamins K and B, which are normally produced by intestinal bacteria. David’s story reflects the impossibility of living without an immune system in a world full of microbes, as well as a human’s dependence on microbes and what they produce for us. Sadly, David died at the age of twelve from a viral infection a few months after a bone marrow transplant was finally performed.

      2:A Newly Discovered Organ: The Human Microbiome

Invisible Life

      The idea of humans being inhabited by countless microbes invisible to the naked eye is as old as the first microscope. Born in 1632 in the city of Delft, in what is now the Netherlands, Antoni van Leeuwenhoek was a tradesman with a special interest in lens making. His desire to see the intricacies of the cloths he marketed drove him to shape glass rods into spheres using a flame. These almost perfect spheres allowed him to magnify not just threads, but anything else he wanted to view СКАЧАТЬ