By building a gigantic petri dish, researchers from Harvard Medical School and Technion-Israel Institute of Technology have produced an incredible visualisation showing bacteria as it mutates to become resistant to drugs.
The new study, published today in Science, is the first large-scale demonstration showing how bacteria react to ever-increasing doses of antibiotics, and how these relentless microbes exploit Darwinian selection to adapt to — and even thrive within — the very medicines meant to kill them.
“What surprised me most about it was that we could actually see evolution happening in front of us,” co-author Michael Baym, a postdoc at Harvard Medicla School, told Gizmodo. “Here were the abstract diagrams we’d been drawing for years, come to life.”
Each year, around 700,000 people die around the world from untreatable bacterial infections, and antibiotic-resistant superbugs could kill upwards of 10 million people each year by the mid-21st century. Just today, the UN announced a high-level meeting to discuss possible strategies and countermeasures.
Baym worked with Roy Kishony of Technion-Israel Institute of Technology and Harvard Medical School on the experiment. They call their giant petri dish the Microbial Evolution and Growth Arena, or MEGA for short. It’s a rectangular platform, two feet wide and four feet long, filled with a gelatinous substance known as agar, a seaweed-derived substance that’s commonly used to facilitate microbial growth. Using the MEGA-plate, the researchers were able to watch antibiotic resistance develop in Escherichia coli.
They divided the MEGA-plate into several sections, each of which was saturated with varying doses of antibiotics. The ends of the platform contained no antibiotics, allowing the bacteria to thrive; these areas represented the starting line. But the adjacent inner sections contained a small amount of antibiotic—just enough to kill the E. coli. Moving inward, each subsequent section of the MEGA plate was treated with a ten-fold increase in the dose of antibiotics. At the very core of the dish, there was 1,000 times as much antibiotic compared to the areas with the lowest dose.
For the next two weeks, the researchers watched — and filmed — as the bacteria died, survived, and adapted to the increasingly poisonous conditions located at the borders of their immediate perimeters. The resulting timelapse video literally shows Darwinian processes at work in a process that would normally remain invisible to the human eye.
As the two-week experiment progressed, the bacteria spread until they reached a potent concentration of antibiotics beyond which they could not grow. That is, until mutants — armed with the specific set of traits required to fight off the poison — finally emerged. This often didn’t take long. At each concentration level, a small segment of bacteria adapted to the hostile conditions, the result of successive accumulated genetic changes.
Once settled in the new section of the MEGA-plate, these tiny populations of antibacterial-resistant mutants were able to grow. When they reached the next section of the platform, the pattern repeated itself. The descendants of this initial group of mutants were able to move to areas filled with higher concentrations of antibiotics. Eventually, multiple lineages of mutants competed for the same space, with winning strains moving on to areas with higher drug doses.