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Project Summary

Difficulty	6
Time required	Long (a couple of weeks)
Prerequisites	Familiarity with sterile laboratory technique is a big plus.
Material Availability	Specialty items
Cost	Average ($50 - $100)
Safety	Standard precautions for handling bacterial cultures.

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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.

Disclaimer: Science Buddies occasionally provides information (such as part numbers, supplier names, and supplier weblinks) to assist our users in locating specialty items for individual projects. The information is provided solely as a convenience to our users. We do our best to make sure that part numbers and descriptions are accurate when first listed. However, since part numbers do change as items are obsoleted or improved, please send us an email if you run across any parts that are no longer available. We also do our best to make sure that any listed supplier provides prompt, courteous service. Science Buddies receives no consideration, financial or otherwise, from suppliers for these listings. (The sole exception is any Amazon.com or Barnes&Noble.com link.) If you have any comments (positive or negative) related to purchases you've made for science fair projects from recommendations on our site, please let us know. Write to us at scibuddy@sciencebuddies.org.

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

Career Focus

If you like this project, you might enjoy exploring careers in Materials Science.

Industrial Engineer You’ve probably heard the expression “build a better mousetrap.” Industrial engineers are the people who figure out how to do things better. They find ways that are smarter, faster, safer, and easier, so that companies become more efficient, productive, and profitable, and employees have work environments that are safer and more rewarding. You might think from their name that industrial engineers just work for big manufacturing companies, but they are employed in a wide range of industries, including the service, entertainment, shipping, and healthcare fields. For example, nobody likes to wait in a long line to get on a roller coaster ride, or to get admitted to the hospital. Industrial engineers tell companies how to shorten these processes. They try to make life and products better—finding ways to do more with less is their motto.

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