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Materials:
- Compound light microscope, like THIS or any of THESE.
- slides
- coverslips
- dropper
- plain yogurt
- collection vial or cup
- toothpick
Procedure:
- Find a small vial and clean it thoroughly. If a collection vial is unavailable, a
plastic cup will do. Make sure ALL soap is completely rinsed off.
- Put a small amount of yogurt in the container, and put it aside in a dark, relatively
warm area. Leave undisturbed for at least 24 hours.
- After the time has past, take a small sample with a toothpick and place on a slide. If
the sample seems too thick, dilute with a drop of water. Next, place a cover slip on
top.
- First observe the bacteria at low power 100X to find a good place to start looking. The
diaphragm setting should be very low (small) because these bacteria are nearly
transparent.
- Switch into the highest power to identify the bacteria according to arrangement.
Bacteria are classified as follows:
First observe the way the bacteria are arranged:
- paired = diploe
- chained = streptose
- clusters = staphyle
Next observe the shape of the bacteria:
- round = coccus
- rod = bacillus
- spiral = spirillum
From here you can identify any bacteria you might find. For example, a common inhabitant of
yogurt is a paired, round bacteria or diplococcus.
Be sure to clean the collection vials and slides thoroughly after usage.
Questions:
- How many kinds of bacteria could you find?
- What are doctors looking for with strep throat?
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