The approach, when developed more fully, could potentially provide information where existing forensic techniques fall short, says Martin Blaser, a professor of medicine and microbiology at New York University. “When you just swab the skin, you get at least 100 times more microbial DNA than human DNA,” he says, so less material could give investigators a stronger signal.
Blaser also notes that fingerprints can’t be accurately read if they’re smudged, while a smudged print could still contain enough microbes to analyze. “The microbiome is us–it’s just another form of fingerprint, just like genomic DNA is us,” says Blaser, who wrote an accompanying commentary to the study, both published in The Proceedings of the National Academy of Sciences.
So far, though, a lot of questions remain about how accurate the technique can become. “We did these studies as a proof of concept,” says Fierer. “Now we need to do the hard work.”
For one thing, it is unclear whether an individual’s microbial signature could be retrieved if another person has touched the object being sampled. Another open question is just how stable an individual’s microbiome truly is. Antibiotics, for example, change an individual’s bacterial profile, although nobody knows for how long. A key step to developing the needed level of confidence, says Fierer, will be to expand the database of microbial communities found on individuals’ hands. Being able to compare a profile to a large number of other profiles will provide a baseline for extracting the truly individual elements.
However, says Relman, “the very reason that makes it more complex gives it all kinds of value that DNA will never have.” For example, he says, a person’s microbiota can reveal not just his or her identity–it can also give clues as to what that individual tends to eat, for example, or where he or she works or lives, so researchers could determine how the types of microbes carried on the body are dependent on such factors.
“I think this is the beginning of the process,” Relman says. “But we are going to need a lot more sources of the variation before we can still see the individual shining through.”