Bizarre Microbiology: Criminal Microbes

Fingerprints can help catch a culprit, but what about their microbes? Luke McNally, from the University of Edinburgh, takes Chris Smith through developing techniques that could use microbes to catch a criminal.

Luke - We’ve talked a lot about the good things our microbes can do for us. Good bugs in our microbiome but one negative is if you commit a crime it's likely they're going to get you caught soon. And so what we're finding is that actually microbial forensics is one of the most exciting areas for use of microbes. There's a few different ways that they might get you caught. The first thing, and probably the most advanced area in microbial forensics, is in trying to time when someone died in, for example, a murder case.

Historically we'd look directly at a body and say “oh, well you know the signs of rigor mortis. So the person has at least been dead for this long”. Or if a body has been outside for a really long period of time, via what insects are consuming it you can tell how long it's been dead. Well there's a similar thing that happens with your microbes. So once you die your microbes start eating you. There’s no immune system to block them anymore. Lots of the microbes that are in our gut, they'll happily sit there once our immune system is keeping them under control, but as soon as that's not the case they'll begin to eat you and consume nutrients. And so what we see is this kind of a clock of microbes that runs as a body is decomposing, both from the bugs within you and from bugs that come from outside. And so that can give us a really tight timeframe on how long it is since a murder occurred, for example.

But the other thing that microbes can tell us is who's been in contact with whom or, for example, where someone has been. If two individuals shake hands, if you sequence the bacteria from the hand of one of those people you can tell who would they shook hands with them. Communities that are on us are like our fingerprints. So just like DNA fingerprinting has been used in terms of measuring our DNA and using that to tell who's committing crime and we can use DNA fingerprinting of our microbes in just the same way.

Adam - And we can open up a whole new Crime Scene Investigation TV show…

Luke - Exactly!

Adam - ...CS Microbe!

Luke - Exactly! This has been entering some of the CSI shows at the moment but the science isn't nailed down hard enough yet for it to really be rolled out at that scale. But it's something that's on the horizon quite soon.

Adam - And I think the final takeaway is don't do crime!