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Germs Are Really All Around Us!

November 22, 2009


Do you have a child that doesn’t understand the importance of washing their hands?  Perhaps because germs appear to be invisible you child doesn’t think it will effect them.  Or have they gotten to the stage that they know more than mom and dad?  Try this experiment with your child, it will be eye opening, if not a little gross. What child doesn’t like to create gross stuff?


Most bacteria collected in the environment will not be harmful. However, once they multiply into millions of colonies in a petri dish they become more of a hazard. Be sure to protect open cuts with rubber gloves and never ingest or breathe in growing bacteria. Keep growing petri dishes taped closed until your experiment is done. Then you should safely destroy the fuzzy bacteria colonies using bleach.
Collecting Bacteria Samples
Use sterile swabs to collect bacteria from different locations and then streak each petri dish with your sample. This experiment offers a wider choice of bacteria sampling locations. Your child can swab over doorknobs, bathroom fixtures, animal mouths, etc.

What you need:

  • Prepared petri dishes containing agar medium and nutrients

Petri Dishes with Agar and Swabs – Science Fair Project Kit through Amazon

  • Bacteria collected from anywhere that your child thinks germs like to linger: doorknobs, bathroom fixtures, etc.
  • masking tape and a marker to label the dishes
  • Sterile cotton swabs
  • Bleach

What to do:

  1. The prepared petri dishes should be refrigerated until used and always stored upside down (i.e media in upper dish, cover on bottom). This keeps condensation which forms in the lid from dropping onto and disrupting the bacteria growing surface.
  2. When ready to use, let dishes come to room temperature before taking samples (about one hour).
  3. Before you begin your experiment, have your child wash their hands.  You want your child to get the most out of this experiment, so include them in picking locations for collecting the bacteria.  Where do they think are the cleanest areas in the house? What area are the dirtiest?  Where do they think the samples should be taken? You may want to ask them what do they think the bacteria will look like? What do they think will happen in the petri dishes?
  4. Collect bacteria from each location using one swab for each new spot.  If you have young children, you’ll want to assist them.  Take a waste basket with you so they can easily throw away the swab after each use.
  5. Have your child make a pattern gently across the entire agar surface
    without tearing into it to inoculate it.
  6. Replace cover on dish, tape it closed, and have your child label each dish so they know the location for the bacteria. Store upside down.
  7. Let it grow in an undisturbed warm location, ideally in an environment around 100° F (37° C) – not in sunlight or on a heating register.
  8. You should see growth within a couple of days. The dishes will start to smell which means the bacteria are growing.
  9. Watch it grow with your child.  They may want to draw pictures of how it looks. Can they determine what locations had the most bacteria?
  10. This part should be done by a parent: Before disposing of dishes in the trash the bacteria should be destroyed. Pour a small amount of household bleach over the colonies while holding dish over sink. Caution – do not allow bleach to touch your skin, eyes or clothes. It will burn!

After you do this experiment, you may never have to remind your child to wash their hands again!

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