The Experiment

Safety

While most environmental bacteria are not harmful to healthy individuals, once concentrated in colonies, they can be hazardous. To minimize risk, wear disposable gloves while handling bacteria, and thoroughly wash your hands before and after. Never eat or drink during bacteria studies, nor inhale or ingest growing cultures. Work in a draft-free room and reduce airflow as much as possible. Keep petri dishes with cultured mediums closed and preferably taped shut unless sampling or disinfecting. Even then, remove the petri only enough to insert your implement or cover medium with bleach or 70% isopropyl alcohol. When finished experimenting, seal dishes in a plastic back and dispose. Cover accidental breaks or spills with bleach or alcohol for 10 minutes, then carefully sweep up, seal in a plastic bag, and discard.

  • A little bacteria is not so bad.

  • Concentrated bacteria (a lot of bacteria in a small space) can be dangerous.

  • Do not inhale (breathe in) or ingest (eat) the bacteria samples

  • Do not handle the bacteria samples without gloves on.

  • Discard petri dishes once you have completed the experiment (if you want to save the petri dishes they will need to be disinfected by cleaning with bleach. Soak in bleash or isopropyl alcohol for at least 10 minutes)

Pre-Experiment: Prepare your Culture Dishes

In order for us to grow bacteria, we must prepare sterile culture dishes! To do this, follow these steps:

  1. Melt the agar in a hot water bath or microwave, using the directions on the bottle. Use a potholder to pick the bottle up because it will be hot!

  2. Let the agar cool to around 110-120 degrees. If you do not have a thermometer then just when the bottle still feels warm but is not too hot to touch.

  3. Slide open the cover of the petri dish just enough to pour agar into it. Pour enough of the agar to cover 1/2 of the bottom of the dish. (be careful not to let the mouth of the bottle touch the dish!)

  4. Cover the dish immediately to prevent contamination!

  5. Tilt the dish back and forth gently until the agar coats the entire bottom of the dish. Fill all ten dishes.

  6. Let the petri dishes stand ONE HOUR so that the agar can solidify.


The Experiment:

  1. Using a sterile swab, collect bacteria from your dominant hand. Run the swab across the palm, across the back of the hand, and in between the fingers. Remove the cover of a petri dish and lightly rub the swab across the surface of the agar in a zigzag pattern. Turn the dish a half turn and zigzag again for maximum coverage. Cover the dish again immediately. Label it "Control" with the person's initials.

  2. Now put a drop of soap in your palm. Time for 20 seconds and wash your hands thoroughly. (rubbing front, back, and in between fingers) in warm water. Let your hands air dry, and use a new swab to collect and transfer bacteria s you did in step one. Label this dish with your initials and "soap". example: OH-Soap

  3. Now swab your parents hand in the same way that you did in step 1. Rub the swab in a new petri dish the same way that you did in step one. Cover the dish immediately. Label it "Control" with your parent's initials.

  4. Put a dime sized amount of hand sanitizer in your parents hands and allow them to fully rub it in.

  5. After they have completely rubbed in their hand sanitizer, use a new swab to collect and transfer bacteria as you did in step one. Label this dish with your parent's initials and "hand sanitizer".

  6. Put all of your petri dishes in a dark, warm place.


Middle School (Suggested):


You are going to also set up a sensitivity test.

  1. Use a marker to draw lines on the petri dish lid dividing into two sections.

  2. Label one section with the name of the soap you are testing. Label the other section with the hand sanitizer.

  3. Make a dish of blotter paper with a hole punch (or small square you cut with scissors) and use a pipet to put a couple of drops of soap on it. Allow the soap to soak into the paper, then carefully wipe off the excess. Using forceps (sterilized with alcohol first), place the disc onto the agar in one side of the dish.

  4. Follow the above step with your hand sanitizer too.

  5. Put all your petri dishes in a dark warm place.