Things You'll Need:
- Prepared petri dishes containing agar medium and nutrients. Easily available on the internet.
- Bacteria collected from doorknobs, bathroom fixtures, etc.
- Wax pencil for labeling dishes.
- Masking tape.
- Sterile Swabs.
- Bleach.
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Step 1
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.
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Step 2
When ready to use, let dishes come to room temperature before taking samples (about one hour).
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Step 3
Collect bacteria from each location using one swab for each new spot.
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Step 4
Inoculate each dish by streaking a pattern gently across the entire agar surface without tearing into it. Another common technique is to divide each plate into four quadrants by marking the lid with a cross. Streak your sample in straight lines starting in quadrant 1. Generally, after a few days, quadrant one will show the most growth. Depending on bacteria abundance on the swab, quadrant 4 may show no grow or only a few colonies. It is sometimes easier to distinguish different bacteria types in this low growth, less cluttered area.
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Step 5
Replace cover on dish, tape closed, and label each dish so you know the source of the bacteria. Store upside down.
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Step 6
Let grow in undisturbed warm location, ideally in an environment around 100° F (37° C) - not in sunlight or on a heating register.
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Step 7
You should see growth within a couple of days. The dishes will start to smell which means the bacteria are growing.
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Step 8
Make observations and keep records of what you see growing in each dish. Can you make any conclusions about what locations had the most bacteria?
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Step 9
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!
