Bacteria in Humans and Dogs

Some organisms, like bacteria, consist of only one cell. Other organisms, like humans, consist of trillions of specialized cells working together. Even if organisms look very different from each other, if you look close enough you’ll see that their cells have much in common.

Most cells are so tiny that you can’t see them without the help of a microscope. The microscopes that students typically use at school are light microscopes.

Robert Hooke created a primitive light microscope in 1665 and observed cells for the very first time. Although the light microscope opened our eyes to the existence of cells, they are not useful for looking at the tiniest components of cells. Many structures in the cell are too small to see with a light microscope.
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In this experiment, you will get to observe single-celled organisms (bacteria, actually) that live in the mouths of both humans and dogs using your compound microscope.

1. You’ll need to get your materials together. Be sure to label the Petri dishes and have your other equipment out: the cotton swabs, the canine volunteers and the human volunteers.

2. First, scrape the inside of a volunteer’s cheek use the cotton tip to swab. Swirl the cotton swab onto a Petri dish.

3. Repeat this for the rest of your human and dog volunteers.

4. Find a dark, warm spot for your Petri dishes to live in that won’t be disturbed for at least 24 hours.

5. After a day, remove the Petri dishes and place it next to your compound microscope.

6. Use a fresh swab to move the bacteria from the Petri dish to the slide and use a staining technique (covered in the Microscope Lab).

7. View each of your specimens, recording everything as you go along.

8. So what do you think? Whose mouth is cleaner – dogs or people?

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