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  • Microorganisms are small. So small you can't even see them unless they cluster together.

  • Each of these dots is really millions of bacteria.

  • But down at a microscopic scale, mold and bacteria fight vicious battles.

  • Their resources and territory are scarce

  • and the stakes are survival.

  • Mold has a powerful chemical weapon in its arsenal.

  • I'm Emily, and I'd like to show you Alexander Fleming's famous

  • discovery that bread mold kills bacteria.

  • Here's some fresh bread.

  • I'll add some water because mold loves moisture.

  • Now I need bacteria, which you can find basically anywhere,

  • including in your mouth.

  • This petri dish has a jello-like layer of agar:

  • food for the bacteria in my saliva.

  • It'll take a few days before the colonies of bacteria are big enough to see.

  • Let's set up a place to grow the mold and bacteria in a contained way, so it doesn't spread or infect anything else.

  • These bell jars will help make sure that

  • nothing contaminates the experiment,

  • and the experiment doesn't contaminate anything else.

  • I'm back!

  • Wow! There's a lot of bacteria!

  • Each cell divided and divided and divided to make a colony

  • that we can see now.

  • Some bread mold also grew.

  • Let's see if it can kill some bacteria.

  • I'll take a chunk of bread mold and let it do its work.

  • Legend has it that in Fleming's original experiment,

  • some mold from his lunch sandwich accidentally dropped into his petri dish.

  • Let's take a closer look,

  • and we'll come back later and see what's changed.

  • Under a microscope mold looks something like this yellow model,

  • and mold attacks bacteria cell walls, represented by these cups.

  • Mold secretes a chemical: penicillin,

  • which damages bacteria cell walls, stamping out the competition.

  • This means the bacteria surrounding the mold will die.

  • We're looking for bacterial death around the mold.

  • Do you see where the bacteria have died around the mold?

  • This is called the ring of death.

  • Mold and bacteria have been battling for millions of years.

  • Mold keeps coming up with new weapons: antibiotics;

  • and bacteria keeps coming up with new shields: resistance.

  • Alexander Fleming, after treating wounded soldiers in World War One, was the first person

  • to realize how useful antibiotics are for treating infection.

  • Today we remember him for his discovery of penicillin.

  • I think his experiment is really neat, and I hope you do, too.

Microorganisms are small. So small you can't even see them unless they cluster together.

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