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So what we ended up building was basically a Petri dish, except that it's two feet by four feet.

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And the way we set it up is that there are nine bands, and at the base of each of these bands,

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we put a normal Petri dish thick agar with different amounts of antibiotic.

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On the outside, there's no antibiotic.

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Just in from that, there's barely more than the E. coli can survive.

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Inside of that, there's 10 times as much, 100 times,

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and then finally the middle band has 1,000 times as much antibiotic.

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and then across the top of it, porous and thin agar

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that bacteria can move around in.

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The background is black because there's ink in it,

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and the bacteria appear as white.

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First, you see they spread in the area

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where there's no antibiotic up until the point

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they can no longer survive.

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Then a mutant appears on the right.

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It's resistant to the antibiotic.

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It spreads until it starts to compete

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with other mutants around it.

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When these mutants hit the next boundary,

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they too have to pause and develop new mutations

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to make it into 10 times as much antibiotic.

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And then you see the different mutants repeat this at 100.

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And after about 11 days, they finally

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make it into 1,000 times as much antibiotic

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as the wild type can survive.

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And so we can see by this process

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of accumulating successive mutations

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that bacteria which are normally sensitive to an antibiotic

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can involve resistance to extremely high concentrations

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in a short period of time.