Bacteria may one day help crime scene investigators catch criminals dirty-handed.
Having found previously that everyone’s hands carry a unique bacterial population, researchers at the University of Colorado in Boulder have now shown that the mix of microbes left on a computer keyboard can be used to tell if a particular person had used it.
Their tests, reported online the week of March 15 in the Proceedings of the National Academy of Sciences, raise the possibility that hand bacteria could potentially serve as a new type of fingerprint. Noah Fierer and his colleagues wondered if bacteria could be used in forensic tests when fingerprints fail, such as when the prints are smudged or evidence consists of fabric or other soft surfaces that don’t lend themselves to fingerprinting.
After all, says Fierer, “you only need to smudge a fingerprint, but you can’t sterilize a surface just by wiping it off.”
Fierer and his colleagues swabbed the hands of three people and took samples of bacteria from keyboards used exclusively by each of the three. The researchers then created DNA profiles of bacterial populations from the hands and keyboards. The bacteria on an individual’s keyboard closely matched bacteria on their hands, the team found. And the bacterial DNA remained useful for at least two weeks after swabbing.
In order for bacterial fingerprints to be useful, however, they must distinguish a person from the general population. So the researchers took swabs from nine computer mice and the mouse owners’ palms. The team then compared the bacterial DNA signatures of the mice and palms to a database of bacteria on 270 hands from other people, typically including both of a person’s hands, sampled for the Human Skin Microbiome project to survey the diversity of microbes living on human skin. In all nine cases, the bacteria on a computer mouse were more similar to bacteria from the owner’s palm than to those from any other hand in the database, the team found.
Other researchers wonder if the technique will be successful in the real world. “Right now we really have no idea how unique a person’s skin microbiome is,” says Elizabeth Grice, a geneticist at the National Human Genome Research Institute and one of the leaders of the skin microbiome project. In the new study, the researchers sampled objects handled by only one person, but if two or more people touch an object they may leave behind a mix of bacteria that might resemble a third person, she speculates.
Fierer agrees that much more testing is needed to determine whether bacterial fingerprinting will be a useful forensic tool. The researchers are now trying to determine how many times people must touch objects to leave their bacterial signatures behind and whether bacterial fingerprints can be lifted from cloth or other soft surfaces.