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It's Surprisingly Easy for Mutant Bacteria to Develop Antibiotic Resistance

In just 11 days, bacteria developed resistance to 1000 times the initial amount of antibiotics.

Even bacteria that are sensitive to antibiotics can develop resistance to them. Scientists at Harvard Medical School designed a test using a mega plate, a two-by-four-foot petri dish, to see how bacteria become resistant to drugs. This time-lapsed video, released by Harvard, illustrates the bacteria in white against the black backdrop of the petri dish.

Initially, the petri dish was divided among nine bands, with each section having a different amount of antibiotics. At the outside edges there were no antibiotics. Then, immediately inside that, there was just enough more antibiotic than the e.coli can survive. The next area had 10 times more antibiotics, and then the next had 100 times more, and then there was 1000 times the antibiotics in the center of the dish.

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Over two weeks, a camera recorded how the bacteria mutated and thrived in the antibiotics. Researchers said that the device, called the Microbial Evolution and Growth Arena (MEGA) plate, represented a simple, realistic platform to illustrate the bacteria's evolutionary changes that either allowed them to adapt to the antibiotics or die.

Initially, the bacteria spread in the area where there was no antibiotic, up until they couldn't survive. Then, at the edges of that region, mutant bacteria appeared, resistant to the antibiotic. Those mutant bacteria eventually spread throughout the petri dish, despite hitting the next boundaries at 10, 100, and 1000, where they had to develop new mutations to make it through.

"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," said Michael Baym, study first author and research fellow in systems biology at Harvard Medical School.

Within just 11 days, the bacteria were able to produce more mutant strains capable of surviving an antibiotic dose 1000 times higher than that which killed the initial bacteria at the beginning of the experiment.

Researchers also noted that the initial mutations led to slower growth, suggesting that bacteria that adapt to an antibiotic can't grow as quickly while they are also developing mutations. But after they mutated to become fully resistant, their growth rates went back to normal.

The findings are as fascinating as they are terrifying, showing just how useless antibiotics may become in the face of mutant bacteria.

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