Watch bacteria evolve to develop resistance to increasingly higher doses of antibiotics in just 12 days.
We often read of antibiotics losing their ability to control or kill bacteria and failing to prevent bacterial infections. In other words, the bacteria become resistant to certain antibiotics and somehow find a way to thrive, reproduce or spread. But we have not seen this process actually happening – until now.
Researchers at Harvard Medical School and the Technion-Israel Institute of Technology have just showed how bacteria adapt and multiply in the presence of higher concentrations of antibiotics. To observe how the bacterium E. coli becomes resistant to higher doses of antibiotics, researchers constructed a giant petri dish named Mega-plate and use it for the cultivation of bacteria. Then, they divided the dish into several sections and saturated them with various doses of antibiotic, trimethoprim. Researchers kept on increasing the dosage as they progressed to the center of the dish and ended up on when they reached 1,000 times the initial dose. The area near the outermost section of dish remained free of any drug.
Over two weeks, a camera mounted on the ceiling of the dish kept on taking periodic shots of the petri dish which were eventually stitched together to create a time-lapsed videotape. The video not only revealed how antibiotic resistance happens but also showed how quickly bacteria can evolve resistance to higher doses of antibiotic drugs.
Researchers found that bacteria continued to grow until they reached the antibiotic dose that was too strong for them to survive and spread. However, at each dosage level, a small group of bacteria was able to adapt and survive. In the span of just 10 days, bacteria were able to produce mutant strains that were capable of overcoming even 1,000 times higher dosage of antibiotic. This means new bacteria were developed that were 100,000 fold resistant to the initial dose. Moreover, the fittest mutants were not always the fastest as well. They stayed behind the weaker strains while the weaker strains battled against the high concentrations of antibiotic and allowed the fittest mutants to move on to the next level.
“We know quite a bit about the internal defense mechanisms bacteria use to evade antibiotics, but we don’t really know much about their physical movements across space as they adapt to survive in different environments.” Lead researcher Michael Baym said.
The experiment possibly provides the first large-scale glimpse of the adaptation and survival of bacteria as they encounter increasingly higher doses of antibiotics. This is a concept that is always discussed but never seen before.
“This is a stunning demonstration of how quickly microbes evolve,” said co-author Tami Lieberman. “When shown the video, evolutionary biologists immediately recognize concepts they’ve thought about in the abstract, while nonspecialists immediately begin to ask really good questions.”