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Quirks and Quarks

Identifying criminals by the 'bacterial fingerprints' they leave behind

We leave a trail of these microbes everywhere we go, shedding about 36 million bacterial cells per hour
CBC Radio ·
Researchers are looking at our bacterial fingerprint to track criminals (Benutzerin, cc-by-sa-3.0)

The human body is more microbes than human. If we took all the bacteria off and out of a human body and put them in a bucket, they'd weigh three to five pounds — a little more than the human brain. We also leave a trail of these microbes everywhere we go, shedding about 36 million bacterial cells per hour. Now one researcher is looking at using our bacterial fingerprint to track criminals, when DNA and fingerprinting just won't do.

Testing out the theory

To do the research, University of Illinois at Chicago PhD candidate Jarrad Hampton-Marcell staged several fake burglaries in homes in Chicago and Ft. Lauderdale. The residents and fake burglars swabbed their noses and hands, as well as areas around the home. Then, the 'burglars' were sent in to various homes to touch whatever they wanted, and the researchers came in after to see who robbed which home.

"While we all have what you would consider like a core microbiome, you have these various species or organisms that are unique to you, or basically microbially more abundant in you than anybody else," says Hampton-Marcell.

Microbes illuminated in blue are seen under a microscope.
If we took all the bacteria from a human body and put it into a bucket, it would weigh three pounds - about as much as the human brain. (Alonnardi, cc-by-sa-3.0)

Using these microbial signatures, they were able to guess whodunnit about 70 per cent of the time. And not only could they tell who 'robbed' the place, but they could also pick up certain lifestyle markers, like if the person had been drinking alcohol, taking supplements, had diabetes, or other chronic diseases. 

"When we did our initial study we looked at two individuals, one actually suffered from migraines, which actually showed up in his microbial profile," says Hampton-Marcell. "But we were also able to show that the other individual was actually using alcohol quite frequently."

Building a microbial profile

The biggest drawback was that the microbiome changes every 30 minutes, so the window to do the sampling is small. However, Hampton-Marcell wants to zone in on the key bacteria that make us unique, and find out how to extend that window.

"Let's say you have 2000 unique microbial signatures that are related to you and only you. There may be as little as 10 to 20, maybe 25, that are significantly important in building your kind of microbial profile," says Hampton-Marcell.

"Maybe those 10 or 20 or 25 bacteria might be more important than the others. Maybe they persist for an hour maybe they persist for two hours. We just don't know yet. But it's going to take a lot more fine tuning investigations and more research to really get down to identifying what what's core and what's stable over time."

Another tool in the toolkit

Hampton-Marcell says this is only just the beginning of the research, and he's excited to see where it goes next.

"Just look at DNA, when it was first introduced in the '70s and '80s, it didn't make its way to the courts until the '90s," he says. "For us to get there it's going to take so much work. But the good thing is that we're showing that this is possible."  

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