The effectiveness of household cleaning agents for killing bacteria
The materials required for this science fair project:
- 4 agar petri dishes prepared with blood agar
- 4 disinfected swabs
- 1 bottle of disinfected water
- 4 used plastic chopping boards
- tap water
- 1 bottle dishwashing soap
- 1 bottle of Dettol soap
- 1 bottle of Clorox
- 4 mackerel fish (or any other type of fish)
- 1 knife
- 1 marker pen
1. For this science fair project, the independent variable is the type of cleaning agent used to wash the chopping board – water, dishwashing liquid, Dettol or Clorox. The dependent variable is the size of the bacteria colony in the petri dish. This is determined by measuring the size of the bacteria colony with a ruler. The constants (control variables) are the room temperature, the amount of sunlight and the ingredients in the petri dish agar.
2. The 4 petri dishes are prepared with the blood agar and stored in a refrigerator. The petri dishes are allowed to settle at room temperature before the start of the science experiment, by taking them out of the refrigerator. The petri dishes are labeled A, B, C and D.
3. The 4 plastic chopping boards are also labeled A, B, C and D. One fish is cut and de-boned on each of the chopping boards and left there for 30 minutes before the boards are washed.
4. The chopping boards are cleaned as follows (according to their number) :
1 – wash only with water
2 – wash with water and dishwashing liquid soap
3 – wash with water and Dettol solution
4 – wash with water and Clorox solution
5. The sterilized swab is first soaked with the sterilized water. The swabs are rubbed over the plastic chopping boards and rolled over the petri dishes according to the numbering. For example the swab used on chopping board 1 will be rolled over petri dish marked 1. Ensure that you roll the swab across the entire surface of the agar.
6. The cover is closed and the 4 petri dishes are kept in a cool shaded place for the bacteria to grow.
7. The diameter of the bacteria colony is measured daily for the next 5 days and recorded in the table below .
The bacteria should be destroyed before being disposed of. Pour some bleach into the petri dish to kill all the bacteria before disposing of the dishes in the trash.