When I get ready to order curriculum and supplies before the start of each school year, I like to sit down with my daughter and ask what she would like to learn about that year. I like her input, children tend to be much more eager about learning when it's something that interests them. This year she asked to learn about germs so we ordered a kit called The World of Germs from The Young Scientist's Club's Magic School Bus series (you can check them out here). The last several projects in the kit involved growing bacteria on agar in petri dishes. She had so much fun, she wanted to do more, so we ordered some prefilled agar petri dishes from Amazon (you can order your own here) and decided to design a few of our own experiments. The first thing she wanted to try was testing which of our household cleaners killed germs best and so we set out to design a simple experiment to figure it out.
Our Experiment: Which Natural Cleaners Kill Germs Best?
Then we split a petri dish in half by drawing a line down the center with a permanent marker and labeled the sides A and B. Using a sterile cotton swab (that came with the petri dishes we ordered) we swabbed area A on the counter and gently smeared it all over side A on the petri dish. Then we cleaned area B on the counter with white vinegar and let it dry. Using a fresh sterile swab, we then swabbed area B and smeared it on side B of the petri dish. We replaced the petri dish lid and then it was time to let our bacteria grow. We created our own incubator by putting warm water bottles in a large pot with a lid. We set the petri dish inside and put it in a dark cupboard for a few days, replacing the warm water bottles every few hours to keep the bacteria warm. After about 3 days these were our results:
Side A (our control) grew lots of bacteria. Side B, the side cleaned by vinegar grew only a few colonies. Vinegar appears to be a fairly effective cleaner!
I had her record the results both by drawing a picture and counting and recording numbers of colonies. Then we repeated the experiment 3 times for our other 3 cleaners.
Our ResultsThey all appeared to kill most bacteria. Hydrogen peroxide worked the best. Not a single bacterial colony grew on it's side of it's petri dish!
The essential oil spray was our least effective cleaner, which inspired our next experiment, Do Essential Oils Really Kill Germs and Which Ones Kill Germs Best?
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