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Pop an aspirin, and you know the drug will be metabolized in a few hours and whatever doesn’t go into the bloodstream will be out of you shortly thereafter. But the same can’t be said for probiotics, so-called good bacteria that are ingested or otherwise consumed for health benefits.

Because they’re living organisms, the bacteria are likely to go on reproducing and responding to their new environment in the human gut. And a new study suggests that probiotics might behave in ways that we perhaps didn’t anticipate.


“It’s the first time that we’ve systematically asked the specific question: Do these bugs evolve during the course of treatment?” said Gautam Dantas, a researcher at Washington University in St. Louis and senior author of the study, published Tuesday in Cell & Host Microbe. Dantas and his colleagues believe the answer is yes.

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