If you've ever wanted to watch a superbug evolve before your very eyes, you're in luck. Researchers filmed an experiment that created bacteria a thousand times more drug-resistant than their ancestors. In the time-lapse video, a white bacterial colony creeps across an enormous black petri dish plated with vertical bands of successively higher doses of antibiotic.
The colony pauses when it hits the first band of antibiotic, creating a stark border between the white colony and the black petri dish. Then the bacteria start to edge their way into the toxic soup. More dots appear and they start growing, racing to the next, stronger band of antibiotic. The bacteria are evolving. After almost two weeks of real time have passed, they've become resistant to the strongest antibiotic and completely taken over the kitchen-table-sized petri dish.
We know dangerous bacteria are getting stronger all the time and that it's our fault because of our excessive and indiscriminate use of antibiotics. Each year, 23,000 people in the U.S. die as a result of superbug infections. But we typically don't get to see superbugs created.
For most people, evolution is just conceptual, says Tami Lieberman, an evolutionary microbiologist at MIT. She and her Ph.D. adviser, at Harvard Medical School and Technion — Israel Institute of Technology, wanted something that would make the evolution of superbugs seem more concrete. "The goal was to see evolution, not to abstract it," she says.
Their video and report were published Thursday in the journal Science.
By having the E. coli bacteria grow across bands of increasingly stronger doses of antibiotic, the scientists could make it look like evolution was marching across the dish. But the setup had another effect that the researchers didn't expect. The faster growing colonies of resistant bacteria were cutting off the growth of slower but more drug-resistant colonies and becoming more successful.
When bacteria evolve drug resistance, it usually comes at some kind of cost to the bug. In the presence of an antibiotic, faster growing colonies don't grow as robustly as the slower ones — but that often doesn't matter. If the strain wants to live on, it just needs to be the first to get to the next human or food source. "[This] phenomenon has been very, very tough to study classically," says Michael Baym, the postdoc who built the 4- by 2-foot petri dish in Kishony's lab. In his contraption, it's impossible to miss.
And if scientists can see it, maybe they can start to study it. Using something as simple as a giant petri dish like this could help scientists open up that spatial dimension that has been missing from the lab, says Pamela Yeh, a microbiologist at UCLA who was not involved in the experiment. "Hopefully this will put back in people's minds how important the spatial element can be."
It's possible that there's a lot of research that can be done by getting away from small, classic petri dishes, Yeh says. But for now, Kishony's 2-by-4 is mostly just a demonstration. Hopefully, a useful one, Lieberman says. "Getting more people to understand how quickly bacteria evolve antibiotic resistance might help people understand why they shouldn't be prescribed antibiotics. The drug resistance is not some abstract threat. It's real."
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