Inside those office walls you share with all your co-workers are millions of microbes that share the space with you as well, some of which you brought in with you when you reported for work.

Now, new research says those microbes, tiny bacteria, vary across cities and appear to be determined by the location of the room, instead of the building materials or the inhabitants, according to a story on npr.org.

A team of researchers from Northern Arizona University, led by Gregory Caporaso, collected samples of microbes in three offices in three different cities, Flagstaff, AZ, San Diego and Toronto, for their study.  Collection plates covered with standard building materials were installed on the floors, ceilings and walls of offices, and the researchers collected the samples over four separate six-week periods.

Human skin bacteria accounted for 25-30 percent of the microbial communities in all nine offices, but the majority of the bacteria came from outside of the buildings.  The scientists were surprised to learn that each city had its own unique microbial signature.  The collection plates in the offices in the same cities were more similar in microbial makeup that those from other cities.

The team said they were not certain as to why this happened, but they suspect the microbes migrated into the offices on the shoes of the workers, or possibly in the outside air being circulated for heating and cooling.

The team noted the bacterial communities were not different based on the types of building materials on which they were collected, but did vary based on the location of the room in which they had been collected.

Jack Gilbert, a microbial ecologist and professor of surgery at the University of Chicago, and senior editor of the article, said “This is a benchmark study.  Previous studies haven’t really controlled for a lot of those variables, so most of the results have been assumptions. This is really a wonderful paper because it’s clearing up many of those assumptions.”

Caporaso said they hoped one day the information could be used to construct buildings that contain healthier microbiomes that could be balances with the surrounding environment, to create a healthier work place.