THIS is the second of two posts featuring studies on the human microbiome. In part I we looked at your gut, the relative merits of probiotics, and several studies from the lab of Jeffrey Gordon looking at how the gut microbiome changes in obesity. In this post I will look at some very recent studies that, rather than looking at a whole community of bacteria, focus on one bacterium that is resident on our skin.
This is perhaps seemingly at odds with the message that I conveyed in part I, which focussed on large, diverse communities; and in which I was sceptical of the real benefit of taking a monoculture as an aid to health. However, in this post we’ll look at what has been learned about the interaction of this single resident species with our skin, how it may help to control your skin’s response to injury, and in fact may even join forces with your body to fight off pathogenic, disease-causing, bacteria. This has potential implications for therapies that destroy the skin microbiome, and for the employment of fastidiously over-hygienic practises that restrict the development of a healthy microbiome.
Our skin, just like the gut, is home to an abundance of microbial communities that differ in composition depending upon location. One of the more prevalent of these residents (also known as commensals) is a bacterium called Staphylococcus epidermidis, an otherwise innocuous coloniser of healthy skin.
The surface of our skin, the epidermis, represents our largest physical barrier against the environment, and plays a delicate balancing act between initiating an inflammatory immune response to invading pathogenic bacteria, or injury, whilst also tolerating the resident bacteria on its surface. Inflammation is an undesirable yet necessary protective response that activates several defensive strategies, from the production of antimicrobial peptides that actively kill bacteria, to directing the secondary ‘adaptive’ immune response, and tissue repair. However, persistent inflammation in the absence of infection leads to poor healing and dysfunctional healing 1.
Two recent studies from the lab of Richard Gallo, at University of California San Diego Medical School, provide a tantalising case for the benefits we may receive from components of our skin microbiome, such as S. epidermidis. In the first of these studies 2, Yuping Lai and co-workers tested the hypothesis that the microbiome may ‘serve to protect the host from unintended inflammatory diseases’. They demonstrate how a product of staphylococci, lipotechoic acid (LTA), suppresses skin inflammation during wound repair, thus preventing a normal inflammatory response from becoming excessive.