Abstract

Objective

The goal of this project is to determine which kitchen cleaning aid is most susceptible to contamination by bacteria, and which disinfectant method cleans most effectively.

Introduction

Bacteria are all around us, and our immune system is generally good at keeping them in check and preventing them from causing us harm. This project focuses on bacteria on ordinary kitchen cleaning aids: the sponges, dishrags, and scouring pads that you use to wash dishes. Since you usually use them with hot, soapy water, they should stay pretty clean, right? Or not?

Find out how clean your kitchen is with this project investigating the bacterial resistance of ordinary kitchen cleaning materials.

Terms, Concepts, and Questions to Start Background Research

To do this project, you should do research that enables you to understand the following terms and concepts:

• bacteria,
• disinfectant.

Bibliography

• Hinman, A., 1996. "What's the Most Unsanitary Spot in Your House?" CNN, March 5, 1996 [accessed October 27, 2006] http://www.cnn.com/TECH/tomorrow_today/9603/sponges/index.html.
• Raloff, J., 1996. "Sponges and Sinks and Rags, Oh My! Where Microbes Lurk and How to Rout Them," Science News Online, September 14, 1996 [accessed October 27, 2006] http://www.sciencenews.org/pages/sn_arch/9_14_96/bob2.htm.
• USDA, 2005. "Fight BAC! Four Simple Steps to Food Safety," United States Department of Agriculture [accessed October, 2006] http://www.foodsafety.gov/~dms/fsebac.html.
• This webpage has background information on bacterial growth. It is from an online textbook of bacteriology, which can be an excellent source of further information on bacteria:
  
• Todar, K., 2002. "Growth of Bacterial Populations," Todar's Online Textbook of Bacteriology, Department of Bacteriology, University of Wisconsin, Madison [accessed October 27, 2006] http://textbookofbacteriology.net/growth.html.

Materials and Equipment

• sample kitchen cleaning aids, e.g.:
  • sponge,
  • dishrag,
  • scouring pad,
  • dishtowel;
• sterile saline solution or sterile liquid bacterial growth medium,
• about 20 sterile test tubes,
• nutrient agar plates (available from Carolina Biological Supply Company and other online suppliers),
• bacteria loop,
• 37°C incubator,
• disinfecting materials, e.g.:
  • dishwashing soap,
  • microwave,
  • household bleach solution (5% in water),
  • air drying.

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Experimental Procedure

1. Do your background research so that you are knowledgeable about the terms, concepts, and questions, above.
2. Distribute the sterile saline solution to sterile tubes (at least 2 tubes per kitchen cleaning material to be tested).
3. Cut small samples of each kitchen cleaning aid and immerse in sterile saline solution.
4. Label the tubes and incubate 48 hours at 37°C.
5. You should also have at least one sterile saline tube with nothing in it as a negative control.
6. After 48 h incubation, you will plate samples from each tube. Label a bacterial plate for each saline tube.
7. Use a sterile bacteria loop to plate a sample from each saline tube. Flame-sterilize the loop before each use, or use disposable loops, one for each tube.
8. Use the quadrant streaking method (see Microbiology Techniques & Troubleshooting).
9. Wait 5 minutes for plates to dry, seal with tape, and then incubate (inverted) overnight at 37°C.
10. Count the number of colonies in each plate and record results in your lab notebook. The plate from your sterile saline solution should have no colonies.
11. Are you surprised at the results?
12. Now try the different disinfecting methods on samples of one or more materials. For example:
    1. Wash with soap and water, then air dry.
    2. Air dry.
    3. Microwave.
    4. Soak in 5% bleach solution, rinse, and air dry.
13. Cut small pieces of disinfected samples, immerse in sterile saline solution, incubate 48 hours at 37°C. Again, prepare at least 2 tubes for each disinfection method.
14. Make sure you have at least one sterile saline tube with nothing in it as a negative control.
15. After 48 h incubation, you will plate a sample from each saline tube. Label a bacterial plate for each saline tube.
16. Use a sterile bacteria loop to plate a sample from each sterile tube. Flame-sterilize the loop before each use, or use disposable loops, one for each tube.
17. Use the quadrant streaking method (see Microbiology Techniques & Troubleshooting).
18. Wait five minutes for plates to dry, seal with tape, and then incubate (inverted) overnight at 37°C.
19. Count the number of colonies in each plate and record the results in your lab notebook.
20. Which disinfection method worked the best?
21. Which disinfection method(s) worked adequately?
22. Which disinfection method(s) did not work adequately?

Variations

• 3-M company makes bacteria-resistant sponges for kitchen use. Compare these sponges vs. plain sponges. Do the bacteria-resistant sponges really work?

• Compare sponges (or dishrags) that have been used for different lengths of time (brand new, 1-week old, 2-weeks old, 1 month old). When should you throw away that old kitchen sponge?
• Compare wooden vs. plastic cutting boards. On which type of surface do bacteria live longer? Which surface cleans up better with soap and water? Design an experiment to find out.

• For more science project ideas in this area of science, see Materials Science Project Ideas.

Credits

Andrew Olson, Ph.D., Science Buddies

Sources

This project is based on:

• Toy, M.A., 2003. "To Clean or Not Too Clean?" California State Science Fair Abstract [accessed October 27, 2006] http://www.usc.edu/CSSF/History/2003/Projects/J1133.pdf.

Last edit date: 2006-10-31 12:30:00