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Oh! Those Shopping Carts! Are They Really Carriers of Bacteria?

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Author: Dr. Muriel Gerhard

Grade Level: 8th - 9th; Type: Life Science, Biology

Objectives:

To determine whether the shopping carts we use in the supermarket are carriers of bacteria. 

Research Questions:

  • What are microorganisms?
  • What are bacteria?
  • Are there useful bacteria? What are examples of these beneficial microorganisms?
  • What are some of the harmful bacteria?
  • What is agar agar?
  • How do we culture bacteria in the lab?
  • Why must you be certain to tape your petri dishes?
  • What precautions should one take to preclude the spread of bacteria?

Background Information: On the information level, this experiment serves to acquaint students with basic information on the culturing and growth of bacteria. They will discover that bacteria are microorganisms that grow everywhere. Yes, on the shopping carts of their local supermarket s. They will view the growth of colonies of bacteria which are readily transferred from the cart handles to their carefully prepared agar plates. They will exercise care by carefully taping the petri dishes closed with masking tape. Bleach will be used to disinfect the working areas. Students will learn that most bacteria collected in the environment are not harmful but they do become a problem when they multiply extensively in the petri dishes. Therefore, following the experimentation and the careful display at the Science Fair, student must discard the petri dishes and contents using bleach. Students may prefer to photograph the petri dishes and their contents and display the photos in lieu of the real dishes. This science fair experiment also serves to acquaint students with the essential processes of sciencing such as the importance of the use of a control, of identifying dependent and independent variables, of data collection, of pictorial and or graphic presentation of data and of being able to make better judgments as to the validity and reliability of their findings. They take on the role of scientists and in the process they learn to act as one.

Materials:

These materials are readily available. You will need:

  • 6 Petri dishes containing sterilized agar containing nutrients which can be purchased directly from Carolina Biological Inc.
  • 6 pairs of plastic gloves
  • sterile swabs
  • disinfectant or bleach
  • wax pencil for labeling the petri dishes
  • masking tape and scissors

Refrigerate your petri dishes containing agar when you receive them. Store them upside down! Cover on the bottom, media on the top.

Experimental Procedure:

  1. Gather all the materials you will need for this project. These include: 6 Petri dishes containing sterilized agar plus nutrients, 6 pairs of plastic gloves, sterile swabs, disinfectant or bleach, wax pencil for labeling the petri dishes, plastic bag to discard dirty swabs, masking tape and scissors
  2. When ready to start the experiment, take the petri dishes out of the refrigerator and let them come up to room temperature. This should take about one hour.
  3. Out you go to the supermarket to collect the bacteria from the handles of the shopping carts. Carry the petri dishes carefully, upside down. When you arrive at the market, put on your rubber gloves, use the cotton swabs to collect the bacteria by brushing the handles lightly and then open the petri dish and swab the swab on the surface of the agar... Toss the swab into a plastic bag. Seal the petri dish with masking tape. Label it. Store it upside down. Repeat this procedure with three different shopping carts. When this is completed, remove the plastic gloves and toss them into the plastic bag to discard when you return home.
  4. When you return home use disinfectant, no not bleach, on your hands. Only use bleach while wearing your gloves to clean the working surface. Bleach burns!!!!
  5. Place you’re sealed upside down petri dishes in a warm place, 100 degrees F. Do not place them in the sun or on a heater.
  6. Reproduce the chart provided below to use to record your observations.
  7. In a few days, you will not only see colonies of bacteria but you will sell them!
  8. Using the data chart which was provided, record your observations. You may want to photograph what is happening or draw sketches of what you are observing.
  9. When you are ready to get rid of the petri dishes use bleach on them but be careful do not get the bleach on your skin!
  10. It is time to review your data and reach a conclusion and write up your report. Be sure to include your bibliography. You may wish to include some ideas as to future research that you would conduct in this area.                                

                             Charting the Data: Observations on Bacterial Growth 

Shopping Carts Number of colonies Size of colonies Sketches
#1      
#2      
#3      

 

Terms/Concepts: Microorganisms, bacteria, colonies, agar agar, gelatin, nutrients.

References:

Maczulac,Anne, Allies and Enemies: How the World Depends on Bacteria , 2009

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