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Hi, are you Mr. Greg Frank?

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Yes, you must be the treehouse detectives.

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I hear you have some beetroot dishes for me to look at.

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This is the one from the treehouse.

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This is the control dish.

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It looks like you've been very careful in labeling these dishes.

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We made sure that each dish was only open for 10 minutes at the same time of day

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so that any microbes would have the same chance of growing.

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And to make sure we were manipulating only one variable,

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we've kept them together for the last 24 hours

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so they have the same growing conditions.

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Let's take a look under this dark field colony counter.

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It will illuminate the colonies and make them larger.

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Wow, this is pretty cool.

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I count 45 colonies in the treehouse dish.

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I couldn't see anything yesterday. What's happened?

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Individual bacterial cells are so small they're hard to see with your eye and even some microscopes.

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However, they grow so rapidly that over a 24-hour period they grow from one to a thousand cells

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and that's what you're seeing in these colonies.

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There are about 15 colonies in my dish.

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The control dish doesn't have any colonies.

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Why do you think the treehouse has more colonies?

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I think it has something to do with the fact that the treehouse is outside.

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That could be one reason.

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Dr. D warned us that it's hard to control everything.

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Perhaps the treehouse is not as isolated as you thought.

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We know that microbes like bacteria and viruses cause diseases,

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but we don't know much about them.

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Can you tell us about microbes?

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It would be very difficult to show you viruses since they are so small,

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but let's take a look at some bacteria.

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We can remove them from the inside of your mouth with this swab.

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RJ told us that there's bacteria inside us all the time, even when we're not sick.

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Let's rub this on a clean microscope slide.

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Before we look at it, let's stain the cells so we can see them better.

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Let's magnify this a thousand times and project it up onto the TV monitor.

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There are lots of different shapes. What's the round one?

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That's a bacteria that we call a caucus.

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That one looks like a cylinder. What's it called?

40
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Yes, we call that a rod shape or a bacillus bacteria.

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That bacteria is round, but it's in chains.

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Yes, we call that a streptococcus.

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Is that like strep throat? Does that mean I'm sick?

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Not necessarily. There are other bacteria that look like the strep throat kind,

45
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but they're actually beneficial to us.

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Are you saying that bacteria can be helpful?

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Most bacteria are good, and in fact, we couldn't survive without them.

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I never thought about bacteria being good.

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Think about termites. As you know, termites eat wood, but they cannot digest it.

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It is the bacteria in their gut that digests the wood.

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This is also true of our own stomachs, where a bacteria known as E. coli

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helps us digest our own food and produce vitamins.

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What about the bad bacteria?

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Some bacteria enters our cells and destroys them from within.

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Others produce very deadly toxins like botulism.

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If bacteria can multiply so fast and cause such damage to the body, how do we survive?

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The body has its own defense system to fight off disease.

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It's called the immune system, and most of the time, it keeps us pretty healthy.

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Sounds like we need to learn more about the immune system. Thanks, Mr. Frank.

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You're welcome. Good luck, and come back if you need anything else.