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RENEE MONTAGNE, host:

Here is a scene you'd know if you watch CSI.

(Soundbite of TV show, "CSI")

Mr. LAURENCE FISHBURNE (Actor): (as Dr. Raymond Langston) The suspect we're looking for is a blonde female.

Unidentified Woman #1: Would you mind giving us your fingerprints and a DNA sample?

Unidentified Woman #2: Actually, yes, I would mind.

MONTAGNE: Sometimes it's not a bad idea for real suspects to say no. Police use DNA from blood or skin samples at a crime scene to identify criminals. Most of the time, this analysis is done on human DNA.

NPR science correspondent Joe Palca reports that scientists also think DNA from bacteria may someday find its way into the courtroom.

JOE PALCA: Most of the cells in the human body are human, right? Wrong. Turns out, the human body is awash in bacteria, in our gut, on our skin. In fact, there are many more bacterial cells in and on our bodies than human cells.

Professor NOAH FIERER (Biologist, University of Colorado, Boulder): As far as I'm concern, the human body is just a large microbial habitat.

PALCA: Noah Fierer is a biologist at the University of Colorado, Boulder. Microbes like bacteria are his thing.

Prof. FIERER: But most of these are harmless, and some of them may actually be beneficial. So it's nothing to be paranoid about.

PALCA: Scientists have recently become very interested in the variety of bacteria that colonize us, because they feel it may explain why some people get sick more than others or some people gain more weight than others.

Fierer's been studying the bacteria on our skin. There are about a hundred different kinds, and that gave Fierer an idea.

Prof. FIERER: We leave this trail of bacteria everywhere we go, and the idea was could we use this trail to identify who had touched a given object or surface?

PALCA: The reason this bacterial trail could be used to identify someone is that we differ in the kinds of bacteria we carry around.

Prof. FIERER: The bacterial communities on your skin are very unique to each person.

PALCA: And there's another factor that makes bacterial analysis a potentially useful tool: Our unique bacterial communities dont change very much over time.

Prof. FIERER: The bacteria where youre going to find on your hand today are going to be pretty similar to those we'll find on your hand four months from now.

PALCA: So here's how it would work: Let's say you wanted to find out who's been using a particular office computer.

Prof. FIERER: We could swab a keyboard key, for example, pull the bacterial DNA off that swab, and then identify all or nearly all of the bacteria that make up that community.

PALCA: So that's what they did. They swabbed individual keys from three personal computer keyboards.

Prof. FIERER: And then matched those keys to the bacteria on the fingertips of the owners of the keyboards. And we showed that we could basically identify whose keyboard it was pretty well.

PALCA: Fierer then tried a similar experiment with people's computer mice, and he found he could match the mouse to the owner. The findings appear in the current issue of the journal PNAS.

In one final experiment, Fierer found that they could still perform an analysis of bacterial DNA two weeks after it had been left on a surface.

Fierer says he's already had some informal discussions with law-enforcement agencies about his bacterial ID techniques, and there's been some interest in this approach. But Fierer's the first to say it's not ready for the courtroom, yet.

Prof. FIERER: There's a lot of work that we need to do to figure out how accurate it is and what are the limitations and so forth. But, yeah, it's encouraging. It does seem like we can actually take advantage of that uniqueness of our bacterial communities.

PALCA: Note to all you potential criminals out there: This is just another reason to wear gloves before committing a crime.

Joe Palca, NPR News, Washington.

(Soundbite of song, "Bacteria")

Mr. JIM NAYDER (Host, "The Annoying Music Show"): Bacteria, bacteria, you might not see them, but they're there. Bacteria, Bacteria...

MONTAGNE: By the way, that music comes to us via Twitter from "The Annoying Music Show's" Jim Nayder at MisterAnnoying. If you'd like to send us a suggestion, you can write to us at MORNING EDITION.

Youre listening to MORNING EDITION from NPR News.

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