Doctors sometimes find gonorrhea bacteria in the human body.
Now medical researchers at Northwestern University have found human DNA in the gonorrhea genome.
The discovery was detailed Sunday in the American Society for Microbiology's online journal, mBio.
Study co-author Mark Anderson told The Times the work was significant because it helps explain how pathogens (such as Neisseria gonorrhoeae, the bacteria this team studied) and hosts (such as people) might evolve simultaneously.
"If a bacterium has the ability to acquire DNA from its host it can take broad evolutionary steps that have the potential to influence the host-pathogen interaction and thus the course of the disease," he said in an e-mail.
Anderson said the team didn't know how the human DNA functioned in N. gonorrhoeae (that's something he and his colleagues will study in the future,) nor precisely how the DNA got there in the first place.
Scientists have observed similar genetic transfers across species, he said -- including relatively frequent transfers between different bacteria, between bacteria and viruses or between bacteria and other microbes such as yeast. One particularly significant exchange involves antibiotic resistance genes; when bacteria share these, it can make infections harder to treat with antibiotics.
But Anderson said that to his knowledge, this is the first time researchers have observed a direct gene transfer from humans to a pathogenic bacterium. "This is a very rare observation," he said.