For this year's science fair project at school my 9 year old is testing the growth rate of bacteria from different sources. In addition, she selected one of these sources, my cell phone screen, and is testing the growth of bacteria from the screen when dirty, when clean, and with anti-bacterial soap added to the petri dish. The images below show the setup after we collected bacteria using cotton swabs.
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| All petri dishes setup. |
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| Petri dishes swabbed from a doorknob, my keyboard, a clean cell phone screen, and a dirty cell phone screen but with anti-bacterial soap added to the dish. |
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| Petri dishes swabbed from a doorknob, my keyboard, my 6 year old's mouth, and a dirty cell phone screen. |
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| Petri dishes swabbed from a bathroom sink and the floor. |
To get started we purchased a set of petri dishes pre-sterilized and pre-filled with agar. If you are starting from empty petri dishes, here is a great website on how to fill them properly with agar.
As you can see, we placed the petri dishes in a plastic tub with a bright light shining on them to increase to temperature to a stable 85-95 degrees F. Bacteria will grow at lower temperatures, but much more slowly. At the end of the day there wasn't much bacterial growth and at first we thought we did something wrong. But then, just before bedtime, we started to see some growth in one of the plates! Very exciting! Unfortunately for you I'm making you wait until tomorrow to see the results after 24 hours of growth! :-)
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