DIY Petri Dish Experiment

Sometimes I go a little extra with my activities. As a nurse, I want to share with my littles all about their bodies and the world we live in. As we studied France in our France Unit Study, I thought a shout-out to Louis Pasteur would be most appropriate. I found sterile petri dishes on Amazon and decided to create my own experiment for my little ones.

Materials Needed:

  • Petri Dishes
  • Agar Flakes (4 tablespoons)
  • Beef/Chicken Broth (2 teaspoons)
  • Sugar (4 teaspoons)
  • Distilled Water (2 cups)
  • Masking Tape
  • Sharpie
  • Q-tips

Bring distilled water to boil – it needs to be hot enough to dissolve the agar.

Add the agar. Stir here and there until it is dissolved (2-5 minutes), Stir in the sugar and beef/chicken broth. Make sure it’s evenly mixed.

Pour mixture into petri dishes. You’ll want to make sure that you touch as little as possible to avoid contaminating them. 🙂

You want to fill them to pretty close to the top, but allowing a little space for them to breath. Bubbles are ok!

I taped them shut with masking tape and put them in a zip-lock bag so they wouldn’t dry out. I put them in the fridge to allow them to harden (and cold decreases microbial growth).

After a day or two, it was time to inoculate them with our bacteria. The main point of this experiment was to show my oldest how dirty different surfaces were! My baby just thought it was a fun sensory experiment, lol.

Each child took turns to check a surface. We swabbed the toilet, door handle, remote and a chair.

We also did mouth, hands and nose of each child.

Each dish I resealed up and wrote on it what it contained (bacteria-wise). I stored them upside down so that the condensation didn’t affect the bacteria growth. I placed them in a box so that the light wouldn’t hurt the growth and placed them in our July heat (perfect incubator!)

After about a week we took a look at our little dishes. What fun growth!

We examined each container (carefully so we didn’t get sick) and compared the growth from different areas of the house. The toilet was relatively cleaner than the doorknob and remote. My youngest (on bottom shown below) has less bacterial growth on her dishes than my oldest (top dishes shown below). How fun to compare!

Of course we disposed of the dishes properly so that little hands could not get themselves sick. What a fun experiment and a good way to show how important it is to wash our hands – even if you can’t see any germs!

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