Using microbes to track down criminals

Solving crimes by analyzing fingerprints or DNA is now standard practice. A new study, however, tests the feasibility of tracing a criminal using the microbes they left at the crime scene.

As you read this, the number of microbes inside of you and on your skin roughly equals the number of cells in your body.

In some ways, we are as much microbe as we are human.

Collectively referred to as our microbiome, a lot of scientists are becoming ever more interested in how these microscopic stowaways impact our health.

For instance, gut bacteria appear to have surprising connections with a range of diseases, such as diabetes and some psychiatric conditions.

The manipulation of bacteria in our gut could potentially be a useful medical intervention in the not-too-distant future.

Similarly, the bacteria on our skin and in our airways have a complex relationship with our health. Some can be considered friendly, protecting us from other pathogens, while others can cause deadly infections if they enter the bloodstream.

Using the microbiome to fight crime

Researchers from the University of Illinois at Chicago are approaching our microbiomes in a wholly new way. They are asking whether the distinct range of microbes that a criminal leaves at a crime scene might be used to track them down.

Their most recent study, titled "Microbial signatures as trace evidence in residential burglaries," was presented at ASM Microbe, the annual meeting of the American Society for Microbiology, held in Atlanta, GA.

Jarrad Hampton-Marcell, who presented the findings, explains:

"If an individual's microbial signatures are recovered from a built-environment, the human-made surroundings that we people live in, they can discriminately identify a person among other individuals. The microbiome," he adds, "can possibly serve as trace evidence in forensic investigations."

Incredibly, humans emit approximately 36 million microbial cells into the environment every hour, and everyone has a unique microbial signature. In theory, that is quite a trail of evidence.

To see whether this might be a viable sleuthing tool, the researchers set up "mock burglaries" in 10 homes.

Before and after the burglary took place, the scientists took samples from various surfaces in each home. They also sampled the hands and noses of the homeowners and burglars.

Could this be a viable approach?

In total, more than 8,000 distinct microbial assemblages were identified among the more than 400 individuals who took part in the study.

Next, the scientists attempted to match the microbial signature of the burglars back to the homes they visited. They write:

"Unique microbial assemblages mapped burglars to homes they burglarized with an accuracy greater than 75 percent."

In other words, by assessing the differences between the microbes they found before and after the burglary, they could identify that someone else had been in the home and narrow it down to a specific individual.

"This study is one of the first to use the microbiome as a forensic tool using unique markers rather than variances in microbial community structure," says Hampton-Marcell.

"With further improvement in detection of stable markers," he adds, "the human microbiome may serve as an additional tool for human profiling and crime scene investigations."

So, it might be some time before a criminal's microbial load commits them to jail, but the potential for it to be used in this way seems intriguing. More work is sure to follow.