What Types of Bacteria Are Found in Your House?

Grade Levels: 5 - 10

Bacterial organisms are everywhere. They are in our homes and schools, in our foods, and in the air we breathe. Your body is marvelously designed to fight bacteria when it enters your body through a cut or another means. While some bacteria is necessary in your body, too much, or the wrong types, can cause serious problems.

Bacteria are smaller than cells and often invade cells. If your body can't protect itself through its immune system, the bacteria will eventually destroy the cell.

One of the problems with bacteria is that you can't see it. If you could, you could do a better job of avoiding it. In the experiment described below, however, you get to not only collect bacteria, but see it grow, as well.

You'll collect samples of bacteria from different areas in your home, then allow it to grow in covered petri dishes containing the nutrient agar. Petri dishes are available from biological supply companies. A set of 10 dishes will cost you about $15. Be sure to label each dish carefully so you know from which area the bacteria inside of it was taken.

Some good areas within your home to check are door handles, the insides of your sneakers, staircase railings, bathroom faucets, your teeth, and the computer's keyboard.

Use a cotton swab to wipe the surface you're testing, then wipe the swab gently onto the nutrient gel in the petri dish. Put the cover, also labeled, onto the petri dish and place it in a dark, warm area where the bacteria can grow undisturbed.

Check for bacterial growth every 12 hours for one week. Record any changes in each dish noting the amount, color and shape of the bacteria.

At the end of a week you will be able to clearly see what areas in your home have the most bacteria. You can chart your information, providing helpful information for your parent or guardian.

Make sure you throw away the petri dishes at the end of the experiment. It would be a good idea to photograph each dish at the end of the experiment for your display at the science fair.

An interesting step further would be to test the back doorknob, then wipe it clean with bleach and swab it again and test for bacteria. This would help you to see if the cleaner did its job and killed the germs.

Excerpted from The Complete Idiot's Guide to Science Fair Projects © 2003 by Nancy K. O'Leary and Susan Shelly. All rights reserved including the right of reproduction in whole or in part in any form. Used by arrangement with Alpha Books, a member of Penguin Group (USA) Inc.

To order this book visit the Idiot's Guide website or call 1-800-253-6476.

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