A multi-university team of researchers reports that microbial samples taken from populations living in the U.S. and Tanzania reveal that the microbiome of the human hand is more varied than previously thought. They say that their findings suggest that the “standard” hand microbiome varies depending on location and lifestyle.
The group published their results (“Hand Bacterial Communities Vary Across Two Different Human Populations”) in Microbiology.
Results compared the microbes on the hands of women in the U.S. and Tanzania and found that organisms that have commonly been identified in prior human skin microbiome studies were highly abundant on U.S. hands, while the most abundant bacterial species on Tanzanian hands were associated with the environment, particularly soil.
The scientists from Yale University, Stanford University, and the Johns Hopkins University Bloomberg School of Public Health, took hand wash samples from 15 adult American women and 29 adult Tanzanian women to compare the species of microorganisms present. In the U.S. group, all participants were graduate students, 13 of white European origin, while two were Chinese-American. In the Tanzanian group, all women were caregivers to children under 5 years of age, living in a low-income urban environment.
"If we ever hope to understand how the microbiome affects health and how environmental interactions alter it, we have to expand research to cover different populations,” said Jordan Peccia, Ph.D., from Yale University, who led the work. "The microbial population on the graduate students' hands looks like what we think the hand microbiome 'should look like', but we can't assume that the human microbiome is a standard thing. Our research has shown that the microbial population on the things people use to interact with the environment the most– their hands–is dramatically different between groups."
The predominant microbial groups found on the U.S. hands included members of the Propionibacteriaceae, Staphylococcaceae and Streptococcacease groups of bacteria, similar to those previously found in hand microbiome studies. In contrast, the Tanzanian samples included members of the Rhodobacteraceae and Nocardiodaceae not previously thought to be common colonizers of human skin. These groups are commonly associated with soil and aquatic environments.
The lifestyle differences between the groups are notable. None of the U.S. group was a caregiver for young children and the group spent the majority of their time indoors. The Tanzanian women live in open-air dwellings in Dar es Salaam, Tanzania, and spend large amounts of time outdoors.
“This study utilized pyrosequencing-based phylogenetic library results to assess bacterial communities on the hands of women in Tanzania and compared these communities with bacteria assemblages on the hands of U.S. women,” wrote the investigators. “These results help to expand human microbiome results beyond U.S. and European populations, and the identification and abundance of soil associated bacteria on Tanzanian hands demonstrates the important role of the environment in shaping the microbial populations on human hands.”