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Individuals Release Their Own Distinguishable Cloud of Microbes, Sequencing Study Finds

NEW YORK (GenomeWeb) – People give off their own distinguishable cloud of microbes, according to a study carried out by researchers at the University of Oregon.

People emit more than a million biological particles an hour by touching surfaces as well as by releasing ones from their breath, clothes, skin, and hair, the researchers noted. It's long been known that people can transmit pathogens to one another as well as to surrounding surfaces, but exactly how they affect indoor air surrounding them has been unclear.

James Meadow, a postdoc at Oregon, and his colleagues collected microbial samples from the air around nearly a dozen healthy people for sequencing while in an otherwise sanitized chamber. As they reported today in PeerJ, the airborne microbes in an occupied chamber differed from those in an unoccupied chamber, and the microbes detected differed from person to person.

"We expected that we would be able to detect the human microbiome in the air around a person, but we were surprised to find that we could identify most of the occupants just by sampling their microbial cloud," Meadow said in a statement.

The researchers first collected bacterial samples emitted by three people who sat in a sanitized experimental chamber for a two-hour and then a four-hour sampling period from air filters and from dishes that collected microbes as they settled as dust. At the same time, the researchers collected samples from an identical, unoccupied chamber.

After sequencing the samples on the Illumina MiSeq platform and performing operational taxonomic unit (OTU) clustering, Meadow and his colleagues found that the bacteria present in an occupied chamber differed from those present in the unoccupied chamber.

All three occupants could be detected above the background airborne microbial communities based on the air filter collections, and two of the research participants could also be consistently detected through the settling dish samples.

Human-associated bacterial taxa were especially abundant in the occupied chamber, the researchers reported. Further, they noted that the bacterial assemblages appeared to be unique to each of the three occupants. For instance, one subject's presence was marked by an OTU similar to Dolosigranulum pigrum, and the only female participant's presence, meanwhile, was associated with a Lactobacillus OTU similar to L. crispatus, which has been found within the healthy vaginal microbiome.

Based on that, Meadow and his colleagues further examined whether people could be distinguished based on the cloud of microbes they leave in their wake. For this second part of their study, they sampled the microbial clouds emitted by eight different people while in the chamber. After sequencing the samples, the researchers focused their analyses on a subset of human-associated bacterial families, including Corynebacteriaceae, Staphylococcaceae, Streptococcaceae, Lactobacillaceae, and Bifidobacteriaceae among others.

Each of the eight participants had their own characteristic concentration of airborne particles, the researchers reported. They added, though, that some individuals' microbial clouds were easier to detect than others', likely due to the concentration of particles emitted and the portion of those particles that were from human-associated bacterial taxa.

Both female occupants, again, were linked with the presence of common vaginal bacteria. In addition, the researchers noted that Corynebacterium and Propionibacterium OTUs were common among all the occupants, though individual OTUs from these genera then reflected certain individual occupants, suggesting to the researchers that species- or strain-level variation in airborne bacteria could inform future studies of the microbial cloud.

In addition to sampling the air in the chamber, the researchers also collected samples from the vents bringing air into and out of the chamber. Two of the eight occupants, they found, could be detected from samples obtained from the exhaust vents.

"It is now apparent, given the results presented here, that the microbes we encounter include those actively emitted by other humans, including our families, coworkers, and perfect strangers," Meadow and his colleagues wrote in their paper.

They added that their findings, if replicated and expanded upon, could have forensic applications for determining whether a certain person was in a specific area.