Bacteria in your toothbrush
The materials required for the science fair project experiment:
- 3 agar petri dishes prepared with agar
- 3 disinfected swabs
- 1 bottle of disinfected water
- 3 toothbrushes
- 1 bottle of Listerine
- 1 tube of toothpaste
- 1 Marker pen
1. For this science fair project, the independent variable is the treatment given to the toothbrush before bacteria samples are taken from it. The dependent variable is the rate of bacteria growth in the petri dish. This is determined by measuring the size of the bacteria colony using a ruler. The constants (control variables) are the room temperature, the amount of sunlight and the ingredients of the petri dish agar.
2. The 3 petri dishes prepared with agar, are stored in a refrigerator. The petri dishes are brought to room temperature before the start of the science fair project by taking them out of the refrigerator and allowing them to attain room temperature. The petri dishes are labeled A, B and C.
3. The toothbrushes are also labeled A, B and C. They are given the following treatment for 5 days before starting the science project experiment.
a. Toothbrush A – is used to brush teeth 2 times a day for 5 days with only water. After brushing the toothbrush is kept in an empty cup.
b. Toothbrush B – is used to brush teeth 2 times a day for 5 days using toothpaste. After brushing the toothbrush is kept in an empty cup.
c. Toothbrush C - is used to brush teeth 2 times a day for 5 days using toothpaste. After brushing the toothbrush is kept in a cup filled with Listerine.
4. The sterilized swab is first made damp with the sterilized water. The swabs are rubbed all over the toothbrushes and then rolled in the petri dishes according to the marking in the petri dish and the toothbrush.
5. The cover is closed and the 3 petri dishes are kept in a cool shaded place for the bacteria to grow.
6. The diameter of the bacteria colony growth is measured everyday for 5 days and recorded in the below table.
Basic safety requirements