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 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 PhD adviser, Roy Kishony at Harvard Medical School, 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 …