Architectural Design Should Promote Microbial Exposure

Children build a lifetime of microbial exposures through encounters with their mother's skin, breast milk, the air and surfaces in neonatal units, that first car ride home, home life and pets, daycare, and then school. And, since humans spend more than 90% of their time indoors, inhaling up to 16,000 liters of air per day, they are continuously exposed to floor and surface dust, and come into direct contact with surfaces, people, and pets.

The microbes in buildings are largely sourced from human and animal occupants and from outdoor microbes that are tracked in or enter via ventilation. They are shed from humans are dominated by skin bacteria, including high enrichments of Actinobacteria and Staphylococcaceae, and also skin-associated yeasts such as Malassezia. Pets contribute Porphyromonadaceae, Rhodocyclaceae, Pasteurellaceae, and Bacteroidetes. Due to the human-driven resuspension of dust and microbes from elevated surfaces and floors, bacterial and fungal concentrations in indoor air are often greater than those in outside air, especially in poorly ventilated buildings.

But this is not necessarily a bad thing. Growing empirical evidence links asthma protection with environmental factors known to supply a microbial exposure. In one important example, children who grow up on Bavarian or Amish farms, where homes are in close proximity to livestock, have significantly lower rates of asthma than the general, nonfarm population. This is likely because some microbes signal white blood cells to form T regulatory cells, which prevent unnecessary immune responses. Early life exposures to these microbes are important for colonizing the gut, where a significant amount of immune training occurs, playing an important role in asthma protection.

According to the researchers, the study of how building design, occupancy, and human activity impact indoor microbial communities can lead to the design of healthier buildings, and better enable studies that seek to identify the sources of beneficial and detrimental microbes. And as the identity, functions, and concentrations of beneficial microbes continue to emerge, focus must be placed on predicting how building characteristics impact building microbes, and how this ultimately shapes the human microbiome. The study was published on July 7, 2016, in Trends in Microbiology.

"One big question becomes how building design (e.g., the geographical layout, the building materials, occupancy, and ventilation) modulates microbial exposure, and our own microbiomes. As more and more beneficial microbes are identified, we--architects, engineers, and the general public--need to think about how we can facilitate our exposure to them,” said lead author Professor Jordan Peccia, PhD, of the Yale department of chemical and environmental engineering. “We can work to develop new, quantitative approaches for solving these problems--something better than our portable air filters and inhalers.”

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Yale University