ALICE: When you think of microbiome, you probably think gut health. But there is new research into the many roles that gut and skin microbes play, including what is called “a glow of health.”

DR. SUSAN ERDMAN: We envision ourselves swimming in a sea of microbes. There are millions, billions of microbes living inside of us, living on the outside of us, living everywhere around us.

ALICE: We’re speaking with Dr. Susan Erdman, a Principal Research Scientist, and Assistant Director, in the Division of Comparative Medicine at MIT, whose research looks at how bacteria and inflammation contribute to systemic health and diseases.

DR. SUSAN ERDMAN: And those microbes are an important part of who we are. They influence how we're responding to the environment. They're influencing things about the quality of our skin, the quality of the membranes in our mouths and around our teeth. When you swallow and things go into your intestinal tract, that mucosa—that membrane that's part of your intestine—that membrane is influenced by the microbes around us.

ALICE: Part of Dr. Erdman’s research is looking at what is called “the big axis.” She's working to understand how the body interacts with the external environment—and the role of microbes in the immune, brain and skin connection.  

DR. SUSAN ERDMAN: We're very, very interested in how a body interacts with the external environment. And a lot of the ways that the body interfaces with the environment involve things that we've taken into the body and then get passed through the body. Our body has multiple ways of interacting with that content that it's exposed to on the outside, and exposed to on the inside. And a big part of that is the immune system. The subtleties of having an immune system that can differentiate between things that are a threat and things that are tolerable to the body are the kinds of subtleties that are the very hard work of the immune system. In a human, these things are very sophisticated. And trying to understand those processes and how the body can manage food, outside contaminants, and so forth—the microbes that are an important part of breaking down food in the gut—and manage to reconcile all of that in a way that it doesn't inflame itself to death is a big challenge for the immune system. So the immune system is really a huge friend to us. And when the immune system goes awry—think autoimmune diseases—it can do very, very destructive things. We became really, really interested in the immune system, and how the immune system can begin to keep us healthy.

ALICE: The immune system doesn’t operate on its own. It networks with the brain, the gut and even our largest organ, the skin to create a big axis. That axis not only protects you, but enables meaningful interactions with the environment. Interactions that can give you a sense of joy or compassion.

DR. SUSAN ERDMAN: The immune system doesn't direct everything about our body, though. A lot of what is directed by our body is in our brain, and how our brain is processing the interface with the outside environment. We became very, very interested in whether or not those things that the immune system is doing on internal surfaces, like the gut, in terms of trying to manage the activities of the microbes that have to digest the food—the food that's coming in from the outside—and the interactions of the immune system with all of that. We were very interested in those activities and the brain, and that big picture axis between the brain and the activities of managing the immune system with the external interface of the environment, which could be inside the body in the gut or on the outside with the skin—we hypothesized that those are the most interesting activities for our potential to be as effective in our interactions with the environment as we can possibly be, for things that derive a sense of joy and purpose in our living, that help us unify our activities beyond ourselves with other members of our group—to extend even to empathy, compassion, caring for others.

ALICE: And it turns out, microbes are a critical part of the big axis!

DR. SUSAN ERDMAN: We hypothesized all of these things were driven by how effectively our bodies were managing these relationships between the microbes, the immune system, and the brain—that this axis that is part of a fundamental part of who we are that could be traced to similarities—even with a species of animals that are so simple—types of worms—that are so simple that, literally, they are a tube. All they have is their external and internal environment and processing—that those kinds of networks inform fundamentally big decisions about what we're doing with our world, how we're caring for others in the community, and so forth. Our research, then, is summarized, or boiled down to, trying to pick apart these relationships. How could we tweak the microbes? How could we tweak the immune system? How could we tweak those relationships with the brain, and the connections between the brain and the gut, or the brain and the skin, for our ultimate benefit? That's the nature of our research.

ALICE: Don’t fear those microbes on your skin, they are important for how you look and how you feel. Some microbes on your skin can impart what Dr. Erdman calls “a glow of health.”

DR. SUSAN ERDMAN: When we think about how our bodies are interacting with the environment, an important part of that interaction is the character of all of what they call epithelial surfaces. So that's the skin. And so in a very simple, mechanical way, how the microbes interface with our bodies is influenced by the health of our skin, and the mucous membranes within our body. And really, in the bigger picture, they're sort of all one and the same. We became very, very interested in the idea that when a baby is first born, and is very naive—comes into the environment with almost no protections—that those microbes that are the very first microbes to begin to colonize an infant after it's born are very important in how the future relationships with the outside environment will happen, even extending to decisions that those infants might make—decisions in their brains—and then the character that they evolve over their lifetimes as they become adults. And we had a hypothesis that these first microbes are very, very meaningful in establishing those connections. And it has some very tangible, very outwardly visible, benefits associated with it. And one of those benefits is that some of the microbiota that are common to an environment that connects with breast milk and the feeding of breast milk—or alternatively, fed by the proteins of milk—are the kinds of microbes that help make a skin surface healthy, resilient to outside damage, and so forth. So our simplistic way of thinking about this was, wow, the mom is giving the baby the nutrients to feed microbes—and sometimes actually giving the baby the microbes themselves—that are helping that infant develop a healthy skin that will protect it from the outside environment.

ALICE: Dr. Erdman found that taking the first microbes you get from mom at birth and putting them in an adult could stimulate healthy skin.

DR. SUSAN ERDMAN: The glow of health series of experiments demonstrated that you can take some of these microbes that come from this mother-infant niche—the microbes that a baby might acquire from its mom, or would get nurtured in those first couple of weeks of living—and that those microbes in an adult might be able to impart the same healthy infant skin effects in an adult that they would in a—than in a newborn baby. And what we found was absolutely amazing—that these microbes stimulate the immune system—and even some hormones, in the brain and locally—that help them make the skin very, very healthy.

ALICE: Dr. Erdman also found that these same microbes could help with rapid wound healing on your skin. Imagine a microbial topical that could one day replace stitches!

DR. SUSAN ERDMAN: But there's so much about a healthy skin that's important to a body in the short term and the long term—how the body functions as a whole. So, for example, we focused on wound repair. We focused on wound repair because we were really interested in the possibility of wound repair serving as a surrogate for being healthy, and living a long, healthy life. So if you imagine a time scale where you have an injury, and that injury repairs very, very quickly—we'll talk about the outside skin for the moment. So, you make a little tiny defect in the outside skin, and it heals really quickly. So really healthy skin is a very important part of staying healthy over a lifetime. And so we went straight for that axis, and started to study what it is that would keep skin that healthy. And we found, through a series of experimental models that allow us to define these things—either things in a Petri dish or, say, mouse models that would allow us to look at what happens when we feed this microbe, and how healthy do these mice stay across a lifetime, and are those things translatable to the next generation, perhaps? And so we became very, very interested in this possibility that this was a key—this healthy, glowing skin, the glow of health—was a key to understanding our bodies and our well-being in the environment in the bigger picture of things.

ALICE: One bigger picture Dr. Erdman discovered is the link between healthy skin and reproductive fitness.

DR. SUSAN ERDMAN: And so we had done a series of experiments in a mouse model system where everything about the mice was exactly the same, except that we added the microbes to the drinking water. And we found some really shocking things. And one of them was that the outer skin coat of the mice—what we refer to as the glow of health—is actually a display of reproductive fitness. That—not surprisingly, that reproductive fitness element was later shown in another series of studies that we nicknamed "Great Balls of Fire." And in that series of studies, what it showed was that this skin health—this really smooth, sleek, shiny, fur coat in the mice—was actually substantiated by these different reproductive criteria. So, the females had bigger litters of babies. They had more interest in caring for their babies, and raising their babies to adulthood. The males had what we call mouse swagger. So those manifestations—that really shiny fur coat was because the skin had changed in a way that you could see under a microscope. And it only took about five days after we started feeding the microbes to the mice to be able to see these changes. So if you took a section of the mouse skin from the mice that were eating the probiotic bacteria, and you took a section of the mouse skin from their counterparts that were treated exactly the same way, that came from the same parents, everything was exactly the same about them, except that they had regular drinking water without the little probiotic boost—the difference of those tissues under the microscope, when you stained them, sectioned them, looked at them histologically with a microscope—the differences were really dramatic. Those differences were a thicker, healthier skin. And the oil glands that produce the oils—the hygienic oils, the oils that help keep skin healthy, and help cultivate other healthy communities of microbes—they were actually changed in a really short period of time after those mice started eating the bacteria. And so there were all of these interesting connections that all went back to how the immune system worked, and how these hormones worked, that all of these things were communicating throughout the body based on simply feeding a single microbe.

ALICE: Are you thinking what I’m thinking? Imagine a probiotic that makes your skin healthier and you more fertile. But there’s more… Dr. Erdman found that the same microbe can actually make you slender.

DR. SUSAN ERDMAN: And so what we had identified was an axis with a microbe, the immune system, and the brain, using a mouse model that allowed us to take this down to the most basic levels of scientific discovery, that opened the door for enormous potential for humans to be able to benefit from those same kinds of things. So, if you were to look at a cage of the mice that were drinking the probiotic microbe, and look at a cage of mice that were matched in every other way but just had regular drinking water, you would discover more than just the super-sleek, shiny, healthy-looking fur coat and skin in the probiotic-treated mice. You would also notice that they were more slender and that they had a more positive, exploratory attitude within their cage. And so, what we found was that abdominal fat, in particular, was reduced in the mice that were—the quantity of abdominal fat, if you were to weigh it or to measure the size of it, was reduced in the mice that had gotten the probiotic. And this was true in both males and females. And the character of that fat was completely different. So, the character of the fat had fewer inflammatory cells, fewer of the cells that create the factors and drive a chronic, smoldering inflammation that is so bad for the body. That—all of that—was decreased in the mice that got the probiotic. So, the underpinnings—this idea that these depots of body fat—unhealthy body fat, inflamed body fat—create this engine of inflammation that makes the heart less healthy, that makes muscle mass decreased, that makes sexual interest drop. All of that stuff was reduced in the mice that had gotten the probiotic. So, the counterpart product was the probiotic-fed mice were slender, they were interested in sexy things, and they had this fabulous, glowing fur and skin.

ALICE: Probiotics are usually a special blend of microbes which work to balance or interact with the different colonies of microbes that live inside and outside of the body. Could the probiotic that Dr. Erdman is researching potentially have the same effect on everyone?

DR. SUSAN ERDMAN: One question embedded in this is not just, is there one super microbe, but does that microbe have the potential to change you, and change things about your skin, or your swagger, or your slender waistline, in spite of recognizing that everybody is carrying a completely different group of microbes with them? So, any of you have microbes that are so unique in their balance and are changing in different ways with each new thing you eat—what you eat for breakfast, what you eat for lunch, what you eat for dinner—it's all incredibly complicated. One of the super-interesting discoveries that we made going through all of this was that this single microbe alone—just adding this one microbe to the mice—had the power to change them, almost irrespective of which other microbes they currently had on board. We were really not expecting that.

ALICE: Wow. I can’t wait for that super microbe to be available. Thanks Dr. Erdman for sharing the new possibilities we are discovering about our powerful microbial partners.

That’s it for this mad tea party. Please check out our other podcast with Dr. Erdman on microbes, oxytocin and love—yes, you heard that right! Check out our weekly newsletter Alice in Futureland on Substack, and our book “Thriving with Microbes.”  And until next time… keep wondering.

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