Like Pigpen's dusty haze or Olaf's personal flurry, each of us is surrounded by our own personal cloud—of invisible microbes. Now, it appears that this unique bacterial signature can be used to identify individuals even after they've left the room.
In recent years scientists have built up all kinds of data about the trillions of microbes that live in and on our bodies and help govern our health, often dubbed the microbiome. They've also known that the human microbiome emits millions of airborne bacteria. But University of Oregon researchers decided to explore the extent to which such microbial clouds are detectable and whether they might carry important information about someone's unique microbial ecosystem.
“From this experiment we've learned that based on the air sampling in a room, you can tell when it's been occupied by a person because of the microbial signature of the air,” explains co-author Adam Altrichter. “And more importantly, we can tell that individuals are unique when they've been in a room, unique in the amount of bacteria they produce and the distinct organisms that they shed.”
We create such clouds in various ways. Microbes like Streptococcus are emitted in our breath, Altrichter notes, while others like Propionibacterium come off our skin. “There's even some indication that members of your gut microbiome could actually make it into the air surrounding you,” he adds. “We're talking about very small organisms, and clothing is not an impermeable barrier.”
Each of 11 volunteers spent up to four hours alone in a room during two sets of experiments. The unique combination of bacteria eight of them produced could be readily distinguished from the microbes of others, enabling the scientists to identify them as individuals based on just their microbial clouds. Other volunteers left clouds that made it clear a person had been present, but not which individual.
The microbial clouds we create have some intriguing potential for future applications. In forensics, for example, investigators might be able to use a cloud like fingerprints to identify where a person has been. “If a person walks into a room, and you're sampling that air afterwards, can you understand who was there based on the bacteria that they are shedding?” Altrichter asks.
Understanding more about how we release our individual microbiomes could also have implications for learning how some diseases spread from person to person—or even helping to fight them. “Thinking about how the microbiome occupies an environment and how that might lead to competition for resources that might make pathogenic strains have a harder time colonizing an area is one way this might prove helpful,” Altrichter says.
However, there's a long way to go before people's clouds can be identified in a real-world environment. The tests, published in the September 22 issue of PeerJ, were done in a very controlled, artificial environment—a small room where the temperature and air were controlled. Surfaces inside the room were wiped down to reduce background bacteria that could confuse the cloud signatures.
Volunteers were surrounded with air filters to collect the particles emitted into the space around them. Petri dishes were also deployed to collect surface biological particles that settled out of the air. Identifying human-made clouds in more complicated environments will be difficult.
“Translating this to someone sitting in an office or a patient in a hospital, where there's going to be a lot of background, will take a lot more,” Altrichter says. “But hopefully as technology progresses and we are able to reduce the lowest detection limits, we can maybe push the envelope a little bit and start to capture a personalize signature in a more realistic environment.”
Another avenue for further research is figuring out why some people's clouds were more distinguishable than others. The team doesn't have definite answers as yet.
“Some individuals may just have a microbial cloud that's very unique to them, where a more generalized microbiome might be harder to distinguish from those of other individuals,” he notes. The rate at which people shed microbes is another factor, and that may vary even in the same person depending on health, diet or simply the time elapsed since their last shower.