Study: Allowing Sunlight In Through Windows Can Kill Dust-Dwelling Bacteria

Microbial communities associated with indoor dust abound in the built environment. The transmission of sunlight through windows is a key building design consideration, but the effects of light exposure on dust communities remain unclear. In a new study published in the journal Microbiome, scientists found that in dark rooms 12% of bacteria on average were alive and able to reproduce; in comparison, only 6.8% of bacteria exposed to daylight and 6.1% of bacteria exposed to ultraviolet (UV) light were viable.

Household dust contains living bacterial species (most diverse and abundant group of organisms was members of the genus Saccharopolyspora) that can be inactivated following changes in local abiotic conditions and suggest that the bactericidal potential of ordinary window-filtered sunlight may be similar to UV wavelengths across dosages that are relevant to real buildings. Image credit: Arek Socha.

Household dust contains living bacterial species (most diverse and abundant group of organisms was members of the genus Saccharopolyspora) that can be inactivated following changes in local abiotic conditions and suggest that the bactericidal potential of ordinary window-filtered sunlight may be similar to UV wavelengths across dosages that are relevant to real buildings. Image credit: Arek Socha.

“Humans spend most of their time indoors, where exposure to dust particles that carry a variety of bacteria, including pathogens that can make us sick, is unavoidable,” said study lead author Dr. Ashkaan Fahimipour, a researcher in the Biology and the Built Environment Center at the University of Oregon.

“Therefore, it is important to understand how features of the buildings we occupy influence dust ecosystems and how this could affect our health.”

Dust kept in the dark contained organisms closely related to species associated with respiratory diseases, which were largely absent in dust exposed to daylight.

Dr. Fahimipour and colleagues found that a smaller proportion of human skin-derived bacteria and a larger proportion of outdoor air-derived bacteria lived in dust exposed to light that in than in dust not exposed to light.

This may suggest that daylight causes the microbiome of indoor dust to more strongly resemble bacterial communities found outdoors.

The researchers made eleven identical climate-controlled miniature rooms that mimicked real buildings and seeded them with dust collected in residential homes.

They applied one of three glazing treatments to the windows of the rooms, so that they transmitted visible, UV or no light.

After 90 days, they collected dust from each environment and analyzed the composition, abundance, and viability of the bacteria present.

“Our study supports a century-old folk wisdom, that daylight has the potential to kill microbes on dust particles, but we need more research to understand the underlying causes of shifts in the dust microbiome following light exposure,” Dr. Fahimipour said.

“We hope that with further understanding, we could design access to daylight in buildings such as schools, offices, hospitals and homes in ways that reduce the risk of dust-borne infections.”

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Ashkaan K. Fahimipour et al. 2018. Daylight exposure modulates bacterial communities associated with household dust. Microbiome 6: 175; doi: 10.1186/s40168-018-0559-4

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