From left: Gloria Dominquez-Bello, Humberto Cavallin, and Jean Ruiz | Boston Atlantic Photography
A look at households in the Amazon River Basin — ranging from huts in a remote jungle village to modern homes in a major Brazilian city — suggests that house walls become reservoirs of bacteria, and hint that changes in home design propelled by urbanization are lowering humans’ exposure to the outdoors, and with it their exposure to the environmental microbes with which they co-evolved. The research appears in the February 12 issue of the journal Science Advances.
The findings pave the way for exploring the possible consequences of altering our human-made environments in ways that diverge from the natural microbial exposure that has characterized most of human existence.
“While human microbes are natural to humans, enclosed environments over-enriched in human bacteria might facilitate transmission of bacteria or bacterial traits, such as antibiotic resistance, for example MRSA,” said Maria-Gloria Dominquez-Bello, associate professor at New York University School of Medicine and lead author of the study. “On the other hand, under-exposure to outdoor natural environmental bacteria may also have effects in the developing infant.”
Scientists from Brazil, Puerto Rico and the United States collected microbial samples by swabbing the floors and walls of living rooms, kitchens, bedrooms and bathrooms (or the equivalent functional spaces) of households located in the rural Peruvian villages of Checherta and Puerto Almendras, the mid-sized Peruvian town of Iquitos (which harbors the largest urban population in the world not accessible by roads), and Manaus, the capital of the Amazonas State in Brazil, a contemporary Western city with 1.8 million inhabitants.
Dominquez-Bello, along with Jean Ruiz and colleagues, discovered that they could predict the functional spaces of homes just by analyzing the microbial samples, and that these predictions became more accurate with increased urbanization. While microbial richness did not change with more modern home architecture, bacterial composition was markedly different.
Urbanized spaces seemed to uniquely increase the amount of human-associated microbes, in particular human mouth and gut bacteria from the Streptococcaceae and Lactobacillaceae families. The boost in these human-associated microbes could increase transmission of potential pathogens and decrease exposure to potentially beneficial environmental microbes.
The decrease in environmental microbial exposure from urban living could have health implications for humans. The “hygiene” or “disappearing microbiota” hypothesis suggests that the reduced pattern of microbial exposure among Westernized populations leads to immune and metabolic disorders that have become the new disease paradigm in the industrialized world.