Gross Science – What’s Growing in Your Home?

WARNING! What you are about to see is not for the faint of heart. Or germophobes. Or people who don’t like to see yucky stuff.

If you have to click away I understand. We’re going to be swabbing household surfaces and seeing what kind of icky things are growing on them.


This experiment is really easy to do and it’s quick, two of my favorite things.

For this experiment you’ll need:

Petri dishes
Agar mix (or homemade*), prepared according to directions and poured into petri dishes
cotton swabs

*Agar is the best growth medium for this experiment but it’s also expensive. You can make your own growth medium easily and it’ll work just fine for this experiment as long as you’re gentle when applying your samples. To make homemade growth medium bring 1/2 cup water to a boil. Add 1/2 Tbsp plain gelatin (usually sold with canning supplies) and dissolve. Add 1/2 Tbsp white sugar and dissolve. Let the mixture cool for 10 minutes and then pour into petri dishes and let solidify for 2 hours. This is enough to fill 4 petri dishes.

Prepare the agar/homemade growth medium.

Collect one sample, then transfer it to a petri dish.

Collect samples by rubbing the cotton swab over household surfaces. Make sure you twist the swab as you collect the samples. We swabbed my son’s toes, a video game controller, the keyboard from the kid’s computer, and a bottle of dish soap.

Transfer the samples by gently (VERY gently if you are using homemade growth medium) rubbing the swab in a zig-zag pattern on the agar, twisting the swab as you go. Write the name of the sample on the petri dish lid.

Store the petri dishes in a warm, dark place and check on them every day.


More neat ideas:
Compare unwashed and washed hands
Compare soap and hand sanitizer
After a week add some antibiotic cream or drops to the samples (drops can be purchased inexpensively in the fish section of pet stores)
Compare a toilet seat to a kitchen sponge
test ice cubes from local fast food places
breathe into the growth medium

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