Frontiers Of Biology

Experimenting with Growing Bacteria at Home

We always hear our mothers telling us to wash our hands with soap and warm water to kill the germs. Let us find out how true this statement is.

For this experiment, we need one 4 inch sized Petri dish, water, 5 grams of agar nutrient, container to boil water, plastic wrap, cotton swab and hand sanitizer.

Step 1

In a container, mix half a teaspoon of agar and a quarter cup of hot water and stir. Bring this mixture to a boil for one minute to completely dissolve the agar. In using the microwave to boil the mixture, be careful not to let it boil over. Be sure that the mixture is clear with no floating particles. Allow the mixture to cool for 3 to 5 minutes.

Step 2

With an adult, carefully pour the solution into both halves of the Petri dish. Get the plastic wrap and loosely cover each Petri dish and leave it to cool and harden for at least an hour.

Step 3

The fun part begins. Collect some bacteria using a cotton swab. This is usually done by rolling a cotton swab in your mouth and lightly rubbing the contaminated end on the gelled agar.

Step 4

Remember you have poured the agar solution into each halve of the Petri dish. That means you have two places to grow your bacteria. Since the first half is tested with a sample from the inside of your mouth, you might want to a sample from other things such as the remote control or the computer keyboard. Or you can skip the mouth test and use other things instead. To get good samples, dampen the end of the cotton swab with water and wipe the end of the swab all over the surface to fully cover the swab with invisible bacteria.

Step 5

After colleting your samples, pull the plastic wrap away from the Petri dish and lightly draw a squiggly line with the end of the swab. Cover the Petri dish again and label the dish with the name of the tested item using a piece of paper taped on top. Place the Petri dish in a safe, dark place to allow the bacteria to grow.

Step 6

On the other Petri dish, do this. Try dropping hand sanitizing gel in the middle of your squiggles. It is said that the antibacterial chemical in hand sanitizers prevent bacteria from growing.

Step 7

Cover the Petri dish again and label it with the name of the tested item using a piece of paper or tape. Place it in a warm dark place. In a few days, varieties of bacteria, molds and fungi can be seen. They will keep growing larger as days go by but there will be no growth on the spots where the disinfectants are. These are called kill zones. Then you can start another experiment on which brand of disinfectant work best.
Safety Measures

It seems that our mothers are right. Remember, bacteria collected in the environment are not harmful. But when grown in Petri dishes and have multiplied, then they can be a hazard. Protect open cuts by using rubber gloves and never ingest or inhale growing bacteria. Keep the Petri dish closed until the end of the experiment. After the experiment, dispose of them by using bleach.