Forensic researchers discovered that computer users' hands leave a distinct bacterial print on keyboards and mice, and that it is possible to identify a piece of hardware's primary user simply by swabbing the peripheral for bacteria. The technique isn't as accurate as fingerprints, but it may someday prove useful for fighting crime.
Our skin houses large bacterial ecosystems and, even after washing your hands, the bacterial community is restored within a matter of hours. Scientists have suspected for some time that we might leave "trails" of this skin bacteria on things we touch during the course of a day, and more importantly, that the bacteria might be traceable to individuals. It's not that each person has a unique bacterial species, but that their ecosystems contain different mixes of species, each present at different frequencies.
It wasn't obvious this would work, though. Scientists weren't sure if the range of bacteria we leave on surfaces would be complete enough representation of what's on the skin to narrow its source down to single individual. The bacteria might also change too much during the time they spend on the surface, obscuring their origins.