Study Finds Soil Bacteria Can Live on Antibiotic Diet

Antibiotics normally kill bacteria. But scientists have discovered that hundreds of bacteria living in dirt not only resist being killed by antibiotics — they use the antibiotics as food.

STEVE INSKEEP, host:

Now let's report on food of a different kind - antibiotics, food for bacteria. That takes a little explaining because antibiotics are supposed to kill bacteria. But scientists were surprised to find that some germs actually love the stuff, they eat it. And it turns out these bacteria are as common as dirt, which is where they live.

Here's NPR's Nell Greenfieldboyce.

NELL GREENFIELDBOYCE: Gautam Dantas of Harvard Medical School in Boston says he and his colleagues didn't have to travel far to make this scientific discovery.

Mr. GAUTAM DANTAS (Harvard Medical School): There's soil everywhere. So we just walked up to, you know, one of the public gardens right outside Fenway Park and took a scoop of the soil.

GREENFIELDBOYCE: They took the bacteria from this dirt, then they put the microbes in a situation where they would not only have to survive in the presence of an antibiotic; the germs would actually have to use the antibiotic as food in order to live. Dantas figured they wouldn't be able to do it and they'd die.

Mr. DANTAS: And so we were quite surprised that those couple antibiotics that we tested initially gave large amounts of bacterial growth.

GREENFIELDBOYCE: The researchers thought, hmm, what's going on? So they went out and got dirt from about a dozen places. Like a pristine forest, a farm, a city park. And they did the same tests with additional antibiotics - 18 in all.

Mr. DANTAS: And in no case did we find an antibiotic that was not eaten by a bacteria.

GREENFIELDBOYCE: It turns out that many different soil bacteria - hundreds - could live on an antibiotic diet. What's more, the scientists discovered something else. If a bug could happily eat one antibiotic, it was also likely to survive when exposed to others.

Mr. DANTAS: On average they were resistant to 17 out of the 18 antibiotics at concentrations used in the clinic. Which is, at least in our mind, that was mind-blowing.

GREENFIELDBOYCE: Now, this study didn't look at bacteria that cause disease in people, but Dontez is a little troubled by the idea that genes for this kind of drug resistance are just out there in the dirt. Since some soil bacteria are related to human and animal germs, he worries that they could pass on their genes for drug resistance.

Mr. DANTAS: That transfer into human relevant pathogens is what we're worried about.

GREENFIELDBOYCE: The researchers describe their work in the journal Science. Gerry Wright studies antibiotic resistance at McMaster University in Ontario. He says when he read this paper his first thought was that he wished he'd done the experiment.

Mr. GERRY WRIGHT (McMaster University): This study is so cool because it's showing us that there is this population of organisms that we had never even thought about before.

GREENFIELDBOYCE: He says scientists previously knew of just a few bugs that could eat up antibiotics.

Mr. WRIGHT: But it was really thought of as more of a parlor trick.

GREENFIELDBOYCE: Now that scientists know that lots of bacteria can do this, Wright says researchers have something new to figure out: exactly how are these germs able to digest the very thing that's supposed to kill them?

Nell Greenfieldboyce, NPR News.

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