Solving crimes with bacterial evidence
It was 121 years ago today. December 7, 1894.
Sir Arthur Conan Doyle, the Scottish physician best known for writing fictional stories about the detective Sherlock Holmes, was spending his final day in New York before heading home to London after a U.S. trip.
If only he’d known then what we know now, because in Sherlock Holmes, Conan Doyle created a forensics expert ahead of his time.
Long before such procedures became commonplace in criminal investigation, Holmes used fingerprints, hair analysis, and blood tests to solve crimes.
Had he been alive today, though, he’d almost certainly have installed a DNA sequencer upstairs at 221B Baker Street.
Not just for its potential in comparing human DNA samples collected from suspects with biological material left at crime scenes, but also because there’s now great potential in using the sequencing of human bacteria for “CSI” purposes.
You see, much like a fingerprint, your microbiome could uniquely identify you.
For example, researchers at Harvard University found that stool samples were particularly reliable.
Apparently your poop has a signature all of its own.
In fact, when the study examined gut bacteria re-taken from participants a year after they’d first “donated”, researchers were able to identify individuals with 86% accuracy.
Everywhere you go, you leave microscopic traces of your bacteria, and you also gather microscopic traces of others.
Dr Josiah Zayner, currently a research fellow at NASA, suggests that banks and convenience stores could purposefully plant rare (but presumably harmless) species of bacteria on their floors which would then get picked up on the soles of criminals’ shoes, allowing investigators to prove that they, or at least their Nikes, had visited at some stage.
What about skin bacteria?
Well, it turns out that a great place to find this is on people’s cellphones, and in a world where more people own mobile phones than have access to working toilets, this could come in handy.
Could your bacteria be used to link your phone to you?
Pretty certainly, according to a University of Chicago researcher who has been able to differentiate between two people with 97% accuracy using only swabs taken from their phones.
Your body’s microbiome contains trillions of bacterial cells and weighs between three and six pounds.
But what happens to the microbiome after death?
The forensics world is extremely interested in this question, and only last year began referring to the “death microbiome” as the thanatomicrobiome (thanatos being the Greek word for death).
It refers to the process in which legions of your own gut bacteria take over your internal organs once you’re deceased.
In a healthy individual the brain, liver, spleen, and heart are free of microorganisms – your immune system keeps them in check.
But after death these bacteria spread, and it turns out that this migration can be used as a pretty accurate measure of the post-mortem interval: a duration which enables investigators to estimate time of death.
A team from Alabama State University (ASU) is working with the Freeman Ranch Body Farm in Texas to understand this better.
The Body Farm houses 150 donated cadavers which are used to study bodily decay. An additional 200 living people have pre-registered as donors.
The ASU team are particularly interested in grave soil, which they say teems with an immense amount of bacterial life after the death of a human.
Applying just the kind of next-generation metagenomic sequencing that we use here at uBiome, they’re developing tests that will enable PMI (post-morten interval) to be estimated with unprecedented accuracy.
All in all, it seems human bacteria is playing an ever-increasing part in the world of crime detection.
But that may not have surprised Sherlock Holmes.
As he might have said to his long-suffering assistant:
“Alimentary, my dear Watson, alimentary.”
Have a great week!
Director of Product, Community, and Growth