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The Human Microbe Trail

It seems that each of us leave a trail of microbes in our wakes all waving signs saying….”Bob was here”….assuming your name is Bob.

Researchers at the University of Colorado, Boulder, have determined that people can be reliably identified solely by the bacteria they leave behind from their hands.

Researcher, Noah Fierer who led the study said:
“Each one of us leaves a unique trail of bugs behind as we travel through our daily lives,”


The researchers swabbed various computer keyboards and mice and found that they could match the germs on them to the hands of their owners with an accuracy of 70 – 90%

Not only that, the bacteria lasted a surprisingly long time. They left the bacteria out in the open expecting few to survive long. I would have guessed that they could last a day or so. Instead they survived for 2 weeks. Pretty hardy little buggers.

You may think that good hand hygiene before every crime would protect you but you’d be wrong. The roughly 150 different species of bacteria on our hands replenish themselves quickly after a good hand washing. You wouldn’t want to get rid of them either. Bacteria are like sharks. A small percentage¬† of them will eagerly bite your head off but the vast majority are harmless, even beneficial.

Actually this is quite an understatement. Life as we know it couldn’t exist without bacteria.

If you killed all your hand microbes, something far nastier may take up residence. This is why I hate all those ant-bacterial products everyone loves selling. Generally speaking, bacteria are our buddies. Actually, we’re THEIR buddies since 90% of the cells in our body are bacterial and not humanial (I know, that’s not a word).

The bacteria themselves aren’t unique to us though, it’s not like I evolved microbe DNA on my hands that no one else has. What is unique, or nearly so, is the mix of species and the amount of each one. In fact, people in general have only 13% of their hand bacteria in common.

The other big angle to this news item is the idea that this technology may one day be used by forensic specialists to identify criminals.

Remember Noah from above? He said: “While this project is still in its preliminary stages, we think the technique could eventually become a valuable new item in the toolbox of forensic scientists,”

It may become valuable, the question is how valuable.

The director of Michigan State University’s Forensic Biology Laboratory, says that it’s “utility in a forensic context is doubtful”.

The bottom-line is that microbial fingerprinting appears unlikely to ever reach the level of certainty we enjoy with fingerprint and dna evidence. These experiments were only 70 -90% accurate after all. If you tried a suspect base on a 90% fingerprint match, you’d be laughed out of court. The same goes for DNA although the culprit may still be someone in your suspects family.

Still I think there can be some big benefits. Bacteria can be used for independent confirmation in conjunction with other methods. Maybe OJ would have been found guilty if they found his bacterial profile…I doubt it.

Sometimes fingerprints are smudged and there’s too little human DNA to test. In these cases bacteria could still be available in abundance and also be the only evidence available.

Bacteria also provide data that fingerprints and DNA could never give like the food you like to eat or where you work or live.

At the very least, I’m sure we’ll hear someone on CSI say: “you know……we found 130 species of your hand bacteria on that knife.”

2 comments to The Human Microbe Trail

  • Drum Billet

    Do the species of bacteria that make their home on human hands not change over time?

    If I commit a murder tomorrow the police would swab the murder weapon (a broadsword) for bacteria and then they would have to find me. It could take them a long time to do that. In the time that has passed I might have got oil, mud, food, acid, etc. on my hands. Would this not change the species of bacteria that live on my hands?

  • Brian the Coyote

    At 70-90% accuracy it is not accurate enough to positively identify a criminal (to court standards, at least) but it should be good enough to eliminate suspects based on having no match.

    Drum Billet has some good points too. How time-stable are the bacterial populations? Could you fool a test by deliberately introducing a different bacterial culture to your hands?

    Like all good research this raises as many many questions as it answers. Thanks for sharing, Bob.

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