Understanding Microbiome Diversity: Is It the Secret to Better Health?
It has been said that “Variety is the very spice of life” — a sentiment that diversity often makes things more interesting, sometimes better. The same is said to be true when it comes to the microbes that live in and on our bodies, namely our microbiomes.
Microbiome diversity is loosely defined as the total number of microbial species found within a given area of the body. Over the past few years, much of the focus has involved the microbiome diversity of the gut, as the microbes that live in the digestive system are of great assistance in the digestion of food and production of metabolites that convey health benefits, such as supporting the immune system, aiding brain function, and more. However, other organs of the body also harbor microbiota that play significant roles in human health and disease.
As it is the largest organ of the body, it shouldn’t come as much of a surprise that the skin houses numerous microbiomes. I say “numerous” because the makeup of the skin microbiome is not homogenous. Thus, it could be argued that there are separate subset microbiomes within the overarching skin biome. A large part of this could be due to “regional” differences in the skin. The temperature, humidity, and types and amounts of body secretions (e.g., sebum, apocrine sweat, etc.) of the skin vary greatly from one site to the next, as can be seen between the back of the hand versus the axilla, for example.
All these factors can create an ecological niche, so to speak, for a different density and composition of bacteria along that body site. It would also impact the composition and density of viruses, fungi, and other microorganisms. Altogether, these changes could have implications on the predisposition for dermatological diseases and conditions in certain body sites and how said body sites should be treated for such.
Alpha Diversity vs. Beta Diversity of the Microbiome
Microbiome diversity is often discussed in terms that describe the differences in the range and composition of microorganisms within a given body part or between two different body parts or two different individuals. Alpha and beta diversity are two types of metrics used to look at microbiome diversity. If unfamiliar with the terms, alpha diversity measures how many types of species live in a given area on a person (or a single sample, if you will). Beta diversity, on the other hand, measures the differences in the microbiome composition between body sites or people (the difference in types of microbes between multiple samples).
Take a skin site like the forearm, for example. Studies have shown that this site has the highest variance of microbiomes when sampled from person to person. Thus, we see a high beta diversity in that area of skin. However, this same site doesn’t usually house a wide range of different microbiomes. Thus, it has a relatively small alpha diversity. Measures of alpha and beta diversity of microbiomes, as well as temporal flux (i.e., the changes to any given microbiome diversity over time), can help assess the characteristics of a species in a particular area of the skin and how they function.
Knowing information about such diversity metrics for any given body site is an important tool in how scientists study the human microbiome and the ways microbiomes might be modulated for skin benefit.
Implications of Changes to Microbiome Diversity
When trying to find ways to leverage information, such as microbiome diversity, for the purpose of developing treatment strategies, we must keep in mind that diversity is only one metric to consider. We must also consider metrics like the overall bioburden of microbes, which is the overall number of microbes that are found in the body site. When washing the face with soap, you might be washing away a whole lot of microorganisms, but it isn’t specific to any type of microbe. Thus, you would reduce the bioburden temporarily but not necessarily the diversity.
Studies have shown that attempts to sterilize a given site of the skin will temporarily reduce the overall amount of microbes, but they will then typically come back in the same proportions. This is because the microbiome is typically driven by both the strains in the given site and the environment of the body site. So, unless you either 1) change the strains by providing a probiotic strain that is able to live and thrive in the given body site and 2) change your habits (e.g., diet, skincare, etc.) to alter the environment of that body site or 3) move to another area of the world where you are exposed to both different microbes and environments, then it is not likely you will see a change in your microbiome diversity.
While changing microbiome diversity for the better might hold the potential for treatment applications, it’s not often a simple task. It can take long-term and consistent use of the right diets, products, and habits to maintain the expected changes for any period of time, especially given the many variables (e.g., skin site, age, gender, ethnicity, geography, lifestyle, etc.) that influence the alpha and beta diversity of microbiomes. However, it is possible, and we have found that to be true in our research around our Xycrobe technology found in the BIOJUVE products. The living Xycrobes have been clinically shown to engraft and thrive both on the surface and in the follicles of the skin, and the adjunct products in the BIOJUVE line produce the environment that allows this to persist.
So, what does all this mean? Is diversity better for the skin? Well, the answer is yes ... and no. In some disease states, such as atopic dermatitis, we can see that the diversity of the skin microbiota in the lesional areas seems to be lower than in nonlesional areas of the skin. But it isn’t just the diversity that is different between these sites. It is also the proportional changes between microbes that are seen. In healthy skin, we tend to see large amounts of C. acnes and very little (sometimes none) of S. aureus. However, the opposite is true in atopic lesions. The question then becomes, is it the low diversity that has led to the skin issue, is it the overgrowth of S. aureus, or is it the lack of C. acnes? Is it all of these? These are the things that scientists are now studying.
In the not-too-distant future, we may be seeing more use of certain microbial strains, or consortia of strains, used to fight such microbiome-related issues. We can start by using metrics like diversity and by looking at the proportions of microbes and how they interact with one another.
Thomas Hitchcock, Ph.D., is the Chief Science Officer for Crown Laboratories, where he oversees clinical development, medical affairs, biological sciences, product development, and research and development for the privately held, fully integrated global company dedicated to developing and providing a diverse portfolio of safe and effective scientific solutions for life-long healthy skin. Dr. Hitchcock is a formally trained scientist with expertise in molecular genetics, microbiology, and dermatology. He has 20+ years of research experience, including basic science, preclinical, and clinical research across several therapeutic areas. He has also been issued patents on his inventions in aesthetic medicine, dermatology, and microbiology. Dr. Hitchcock lectures and presents his research internationally. His work has been published in notable journals such as the “Journal of Biological Chemistry,” “Annals of the New York Academy of Sciences,” “Clinics in Plastic Surgery and Nature,” “Journal of Cosmetic Dermatology,” “Aesthetics Surgery Journal,” “Nucleic Acid Research,” and “Cell Transplantation.” He is also the co-author of the book “Rebooting the Biome”.