These days, almost everything and everyone seem to have a microbial signature, so why not cities?

According to a study published in mSystems, an open access publication from the American Society for Microbiology, cities do have their own specific microbial communities.

However, offices in the same city don’t vary that much in microbial communities; the study was meant to offer insight into what contributes to the composition of microbes in built environments.

After collecting samples from nine offices in three North American cities, the research team led by Northern Arizona University in Flagstaff discovered that human skin has a significant contribution to the makeup of built environment surfaces.

The team also found that the most contaminated surface in an office is the floor, evidently because of soil and other materials that are brought in by the workers’ shoes.

Study author J. Gregory Caporaso, Ph.D., the assistant director of the Center for Microbial Genetics and Genomics at the University, said that in normal conditions, “microbes may be passively accumulating on surfaces in the built environment rather than undergoing an active process.”

For the study, Caporaso and colleagues kept an eye on three offices over a one-year period in three cities, Toronto, San Diego, and Flagstaff. In each office, researchers placed three sampling plates containing two or three swatches of ceiling tile, painted drywall, and carpet.

At the same time, they installed sensors that allowed them to monitor different parameters of the environment, such as temperature, relative humidity on the surfaces of the swatches, light, and occupancy.

Each season, researchers collected the samples and analyzed them with two laboratory techniques called ITS-1 and 16S rRNA gene sequencing to determine the bacterial and fungal communities.

Regardless of the material, floor samples contained the highest levels of microbes. Researchers also found that each of the three cities has its own signature microbial communities.

Caporaso said this was the most interesting finding, especially because even though the offices studied within a city were different in size, ventilation systems, and usage patterns, they still followed the same microbial pattern.

It suggests that “geography is more important than any of these features in driving the bacterial community composition of the offices within the ranges that we studied,” Caporaso added.

Researchers also tested to see if office workers were sources for the microbes found in offices, so they collected human skin, oral, nasal, and fecal microbiome samples. At least 25-30 percent of the office microbiome was determined to come from human skin.
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