Bacteria evolve resistance to extreme doses of antibiotics in just a few days.
Evolution is often thought of as an exceedingly slow process, requiring hundreds of thousands, or even millions of years. But for bacteria, which reproduce once every 30 minutes or so, evolution can occur remarkably quickly. Their propensity for fast evolution means bacteria are capable of rapidly evolving antibiotic resistance — a “significant and growing medical problem across the globe,” according to Gerard Wright, a scientist at the Michael G DeGroote Institute for Infectious Disease Research in Canada.
Now, scientists at Harvard Medical School have created a large device — the microbial evolution and growth arena (MEGA) plate — that allows them to visualize the evolution of antibiotic resistance through time and space.
The rectangular petri dish, more than a meter long, is coated with a gradient of antibiotic doses. The outer edges are antibiotic-free, but moving inward, antibiotic strength increases 10-fold each step of the way. The very center of the dish is a highly toxic zone, seemingly unsuitable for bacterial growth.
Michael Baym, lead scientist on the project, filmed E. coli growing on the MEGA plate over 11 days. The first colonists flourish in the antibiotic-free zones on either edge of the plate, where they quickly multiply until food and space run low. Soon enough, a mutant that can withstand exposure to low levels of the antibiotic invariably arises on the frontline of the culture, and ventures into the unoccupied zone next door to reproduce. Once again, space and food soon become limiting factors for these antibiotic-resistant mutants, and when an even more resistant mutant arises, the next zone over opens up for colonization.
By the end of the experiment, the E. coli had evolved to be 10,000 times more resistant to trimethoprim and 100,000 times more resistant to ciprofloxacin — both of which are antibiotics used to treat bacterial infections in humans.
The video demonstrates visually how, through successive mutations, “bacteria which are normally sensitive to an antibiotic can evolve resistance to extremely high concentrations in a short period of time,” Baym states.
The MEGA plate and experiments are described in detail in a paper published in Science.