Pig-Pen wanders through the frames of the "Peanuts" comic strip trailed by a dust cloud. Turns out this “messy” kid may be all of us.

Scientists at Northern Arizona University say a quarter to almost a third of the microbes found in offices are derived from “personal microbial clouds,” composed primarily of skin bacteria. The research team also discovered individual cities have distinct microbial communities, which are similar from office to office within the same urban area.

“In the United States, humans spend over 90 percent of their time in built environments, such as homes, offices, hospitals, and cars,” wrote the authors of the study, explaining how environmental microbes relate to our health. The countless bacteria, viruses, fungi, and protozoa that reside in the air, in water, on surfaces, and within heating, ventilation, and air conditioning (HVAC) systems shape how susceptible we are to allergies and infections. Meanwhile, the mold that grows in damp HVAC systems, for instance, is a well-known irritant that can affect our eyes, skin, nose, and throats, and even impact our lung capacity.

Yet, we inhale millions of microbes with each and every breath and rarely become sick, so most microbes may not be detrimental to our health. Still, questions remain. If the indoor biological environment contains resident microbes, do they come from the geographic location, the building materials, or the inhabitants? The Arizona research team teased out individual components in the microbial communities (or microbiomes) found in offices of three separate cities to find out.

Personal Cloud

Over a year, Dr. J. Gregory Caporaso, senior study author and biologist, monitored three offices each in Flagstaff, Ariz., San Diego, and Toronto. In every office, Caporaso and his colleagues installed a sampling plate on the floor, ceiling, and wall. Each plate contained two or three swatches of drywall, tile, or carpet, plus sensors that monitored temperature, humidity, light, and occupancy. Collecting samples seasonally, Caporaso and his colleagues used gene sequencing and other laboratory techniques to profile bacterial and fungal communities.

Floor samples, no matter the material, contained more microbes than wall or ceiling surfaces, Caporaso and his co-researchers found. They also discovered the largest source of microbes in each office was from non-human sources.

In fact, for each city they identified a signature microbial community, which suggests geography, more than any other factor, drives the bacterial communities found in each office. This finding was particularly intriguing, Caporaso noted, because the offices in each city were each distinct in terms of size, use, and HVAC system. The Flagstaff offices, in particular, had richer microbial communities than the offices in either San Diego or Toronto, which were more similar to each other, though the researchers do not know why.

Across all nine offices, the researchers identified skin bacteria as the largest human source of office microbes; at least 25 to 30 percent of the office surface microbiome was derived from skin. Nasal microbes also contributed consistently to office surface microbial communities, though to a smaller degree. However, the microbiome of each office was not directly related to its occupants.

“It appears that the personalized microbiomes of the office inhabitants or samplers were not transferred to our office surfaces,” wrote the researchers, who suspect this resulted from a lack of direct contact, since they’d asked workers to avoid touching the sampling swatches.

Still, skin and other human microbes indirectly transferred to these surfaces, suggesting each of us trails the microbes of ourselves, others, and the places we visit. Just like Pig-Pen, then, we live in a cloud of microbial dust.

Source: Chase J, Fouquier J, Zare M, et al. Geography and location are the primary drivers of office microbiome composition. mSystems. 2016.