Microbiome in healthy skin, update for dermatologists

Abstract

The skin is a complex barrier organ made of a symbiotic relationship between microbial communities and host tissue via complex signals provided by the innate and the adaptive immune systems. It is constantly exposed to various endogenous and exogenous factors which impact this balanced system potentially leading to inflammatory skin conditions comprising infections, allergies or autoimmune diseases. Unlike the gut and stool microbiome which has been studied and described for many years, investigations on the skin or scalp microbiome only started recently. Researchers in microbiology and dermatology started using modern methods such as pyrosequencing assays of bacterial 16S rRNA genes to identify and characterize the different microorganisms present on the skin, to evaluate the bacterial diversity and their relative abundance and to understand how microbial diversity may contribute to skin health and dermatological conditions. This article aims to provide an overview on the knowledge about the skin microbiota, the microbiome and their importance in dermatology.

Figure 1

Topographical distribution of bacteria on skin sites.8 Reprinted by permission from Macmillan Publishers Ltd: Nature Reviews Microbiology, ‘The skin microbiome’, Grice EA, Segre JA., Nat Rev Microbiol. 2011 Apr; 9(4): 244–253.

Figure 2

Interpersonal variation in the skin microbiome.8 The microbial distribution of four sites on four healthy volunteers (HV1, HV2, HV3 and HV4) is depicted at the antecubital fold (inner elbow; part a); the back (part b); the nare (inside the nostril; part c) and the plantar heel (bottom of the heel of the foot; part d). Skin microbial variation is more dependent on the site than on the individual. Bars represent the relative abundance of bacterial taxa as determined by 16S ribosomal RNA sequencing. Reprinted by permission from Macmillan Publishers Ltd: Nature Reviews Microbiology, ‘The skin microbiome’, Grice EA, Segre JA., Nat Rev Microbiol. 2011 Apr; 9(4): 244–253.

Figure 3

Factors leading to dysbiosis and innate immunity response of the skin.

Figure 4

Distribution of pH and temperature of a healthy human skin.79 Adapted by permission from Cambridge Edition: Cambride University press, ‘Inhabitants of Humans: Their Ecology And Role in Health And Disease.’ Wilson M. 2005 Apr; 9(4): 244–253.