“People take probiotics for their gut, and then they turn around and use Purell,” says Julia Segre. While the public is beginning to recognize some internal microbiomes as beneficial, there’s still a sense that the skin should be germ-free. Segre and colleagues have been studying the ecology of bacterial communities on the human skin, and hope that this can change perceptions regarding healthy skin.
Segre began by conducting a survey of microbes found on the human skin. “Feet is where you see all your diversity,” she says, and it’s also where you see most fungal involvement. However, she has not yet found archaea on the human skin. There is more similarity according to body part than according to individual, Segre has found, meaning that the community inside your elbow has more in common with the community in someone else’s inner elbow than the community in your own ear. However, skin microbial communities are still specific to individuals and fairly stable over time. P. acnes and S. epidermidis are the most common, and though we call them by the same name, strains can differ by 10-20%, including variations in drug resistance and other important traits. While abundance of organisms is largely dependent on access to resource abundance, the strain identity is closely linked to individual. The stability of these strains and communities provide make it interesting to think about the possibility of “probiotics for the skin” – would new strains or species be able to take hold in these stable microbiomes?
Segre used her insights to examine atopic dermatitis (eczema), which affects 15% of US children. During a flare up of the disease, Segre found an increase of Staphylococcus on patients’ skin, which returned to normal levels after the flare. Further analysis identified a few key Staph strains in all cases, emphasizing that different strains can matter functionally. Segre is also working to incorporate viral diversity into our understanding of skin microbial ecosystems.