We are also making six replicates of each test. In our previous post, we determined that we will need six groups of plates - one group for each test condition. Also, don’t play with the spray bottle! Ethanol will cause plenty of misery if it gets in your eyes. Make sure you have an adult around if you’re going to work around open flames. This should help prevent germs in the air from settling on the meat or agar. As it warms, this air rises, creating a small updraft - an air current moving toward the ceiling. Candle flames bring in cooler air from below. Lit candles placed around the experiment also helped to keep other microbes away. And I used a spray bottle containing 70 percent ethanol - a type of alcohol - and 30 percent water to clean any surface used, wiping everything dry with fresh paper towels. Any glass or spoons were boiled in a pot of water with a little bit of bleach, to ensure they were completely clean. To lessen the chance the experiment would be contaminated, I wore a lab coat and lab gloves (you can buy gloves made of latex or nitrile that you throw away after one use). For our experiment, though, we had to make sure that the bacteria that grew on the plates came only from the dropped food - not from anywhere else. They’re on the floor, in the air and on your hands. I used a system for mine that included the floor I was testing (clean or dirty), the time (five or 50 seconds) and the plate number. Before you start your experiment, label your petri dishes with a permanent marker to make sure you can keep track of which plate is which. Once the dishes are dry, they can be used right away or stored in plastic bags in the refrigerator. The agar will start to firm in about 10 to 20 minutes.
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