Forensic investigators may get another technique for their tool kit. Much like fingerprints and DNA, the ecosystems of bacteria that live on our skin—and get left behind on everything we touch—are unique and descriptive, meaning that they could provide a new way to establish identity.
Efforts to characterize bacterial populations on human skin have turned up a surprising level of variation from person to person. “Once you look at these microbes at the species level, we are all pretty much distinct,” says Noah Fierer, a microbial ecologist at the University of Colorado at Boulder. To test whether skin-associated bacteria could be tapped for forensic use, Fierer and his colleagues swabbed the fingertips of three people and their computer keyboards and then sequenced short stretches of the bacterial DNA. They found (pdf) that they could match the genetic material on a keyboard to that on an individual’s skin. Better yet, Fierer and others have shown that resampling a person after a few months turns up a very similar set of bacteria, indicating that the denizens of our skin are largely permanent residents.
Bacteria-based forensics is not ready for the courtroom yet, Fierer says. Further testing will be required to determine the technique’s accuracy rate. To better understand the differences among individuals, he is exploring how the communities on our skin are shaped by diet, environment, and family. If those factors yield predictable bacterial patterns, they could provide additional useful information for investigators about a subject’s location or habits, although interpreting such data will probably be tricky, Fierer says.