NEW YORK (GenomeWeb News) – In a paper appearing online today in Science, American researchers began unraveling how the diverse and complex microbial communities residing on human skin vary with skin microenvironment, time, and between individuals.
Researchers from the National Human Genome Research Institute, the National Cancer Institute, and the National Institutes of Health's Intramural Sequencing and Clinical Centers used 16S rRNA sequencing and analysis to characterize the microbial communities found at 20 skin sites in ten individuals. Their results suggest that these communities vary depending on whether skin sites were sebaceous, moist, or dry.
And while the team detected some intrapersonal variation, they reported that most individuals tested tended to carry similar microbial communities over time.
"Our work has laid an essential foundation for researchers who are working to develop new and better strategies for treating and preventing skin diseases," senior author Julia Segre, an NHGRI senior investigator, said in a statement. "We hope this will speed efforts to understand the complex genetic and environmental factors involved in eczema, psoriasis, acne, antibiotic-resistant infections and many other disorders affecting the skin."
The Human Microbiome Project is an NIH Roadmap project focused on teasing apart microbial communities on and in the human body in order to get a better handle on how microbes influence health and disease. Last year, Segre and her team published preliminary skin microbiome results, evaluating different strategies for sampling skin microbes on the inner elbow.
For the latest paper, the researchers used 16S rRNA sequences to assess the microbial communities at 20 skin sites in ten healthy individuals. In the process, they generated sequence information for 112,283 16S genes representing 19 bacterial phyla.
Most of the microbes detected came from four phyla: Actinobacteria, Firmicutes, Proteobacteria, and Bacteroidetes. But the microbial composition and diversity varied considerably depending on the body site and skin microenvironment tested.
Whereas bacteria from the Propionibacteria and Staphylococci genera were most common in sebaceous sites, moist sites tended to carry Corynebacteria species as well as some Staphylococci. Dry skin sites, meanwhile, were associated with a mixed bag of bacteria, though the team most often detected Beta-Proteobacteria and Flavobacteriales.
Of all the body sites tested, the inner forearm had the greatest taxonomic richness, harboring bacteria from roughly 44 species-level operational taxonomic units. The retroauricular crease, behind the ear, had the lowest richness at just 15 mean OTUs.
Overall, the researchers noted, sebaceous sites, such as the skin between the eyebrows, beside the nostril, on the back of the head and upper chest, had less species diversity, richness, and evenness than moist or dry skin sites.
When they compared one individual to the next, the team found that some skin sites — including the spaces between fingers and toes — varied greatly from person to person while others — such as the back, nostril, and crease beside the nostril — were relatively similar.
In terms of intrapersonal variation, the team detected less intra- than inter-personal variation in general when they compared individuals' left and right inner elbows, armpits, and inner forearms.
The researchers also did follow-up sampling for five of the individuals four to six months later. Their results suggest that skin areas on the outer ear canal, side of the groin, nostril, and crease beside the nostril were most similar from one time to the next. On the other hand, the researchers found that the microbial communities associated with areas behind the knee joint, inner forearm, and buttock varied most with time.
Four of the five individuals who were sampled more than once carried microbial communities that were more similar to themselves than to other people at the second time point.
"Not only does our work shed new light on understanding an important aspect of skin biology, it provides yet another example of how genomic approaches can be applied to study important problems in biomedical research," co-author Eric Green, scientific director of NHGRI, said in a statement. "This also demonstrates what can be achieved through efforts that pull together researchers from across NIH."
By characterizing microbial communities in healthy individuals, the researchers also hope to gain a better understanding of how these communities shift during disease states — insights that may help in developing treatment and prevention strategies.
"Elucidation of the baseline skin microbiome is a step toward testing the therapeutic potential of manipulating the microbiome in skin disorders," the authors concluded. "Targeted therapies to maintain healthy skin might require not only inhibiting the growth of pathogenic bacteria, but also promoting the growth of symbiotic bacteria."