Bacterial trail may be next forensic clue


Forget fingerprint dusting. Crime-scene drama fans might soon see a new forensic technique debut on their favorite TV series: hand-germ testing.

According to a study published online Monday, bacteria that live on a person’s hands could one day accurately identify that individual. This could come in handy to track down a criminal who has worn gloves, removed prints and other personal physical evidence, or touched surfaces such as fabric on which a fingerprint wouldn’t show up, the researchers said.

The concept, outlined in a paper in the Proceedings of the National Academy of Sciences, relies upon the fact that human beings leave a trail of bacteria on objects they touch and that the mix of microbes on each person’s hand is highly individualized.

“There’s a rain forest of bacteria on your skin,” said lead author Noah Fierer, an assistant professor of ecology and evolutionary biology at the University of Colorado at Boulder. A human hand can contain on average about 100 different species of bacteria, he said, and only about 13% of that makeup is shared between any two people.

Fierer and colleagues compared the bacteria found on people’s computer mice with a database of bacteria collected from the hands of 270 individuals. The bacterial colonies from the computer mice most closely matched those of the owner’s hands, the scientists found.

The technique was 70% to 90% accurate overall, but this could be sharpened as technology becomes more sophisticated, Fierer said.

Other problems would have to be worked out as well. For example, if more than one person has touched an object, it isn’t yet possible to sort out their mixed-up bacterial signatures, said David A. Relman, a Stanford University professor who has studied the signatures left by gut and mouth bacteria.

Also, Relman said, the distribution of bacterial species might change once the microbes have left the human hand, making the pattern less easy to link to a person.

“It’s intriguing because it suggests a new approach to forensics,” said Dr. Martin J. Blaser, chairman of medicine at New York University, who wrote a commentary accompanying the report. However, he said, “this is not ready for prime time.”