; Bacteria Isolation and Staining Lab
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Bacteria Isolation and Staining Lab


A lab covering the basics of making a bacterial slide to view under the microscope. Covers the use of methylene blue stain and heat fixing.

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  • pg 1
									Name: __________________________ Class: _____________________ Date: _____________________

                      Finding Bacteria from a Culture
Looking at a petri dish, you might be able to see lots of circular colonies of bacteria growing. Each colony may
contain millions of individual bacteria cells. The best way to learn more about what is growing in the culture is
to isolate some of the cells and view them under a microscope.
Sampling the Bacteria
   1. Get a clean glass slide. Place a small drop of distilled water on the surface.
   2. Take a metal inoculating loop and put the tip over a flame until it glows.
   3. Allow the metal loop to cool long enough to stop glowing. Place it in an
      empty part of the agar (you should hear it sizzle as it cools.)
   4. Scrape off part of one of the colonies and touch it to the droplet of water on
      the glass slide. The water should appear slightly cloudy.
       -   Warning: If you add too much bacteria, they will clump together,
           and you won’t be able to see them individually!
   5. Burn the rest of the bacteria off the metal loop. Allow it to cool again.
   6. Spread the water/bacteria mixture around the center part of the slide, making a thin film.
   7. Allow the slide to air dry. (This will take a few minutes)
   8. Pass the slide over a Bunsen burner 3 or 4 times to heat-fix the bacteria. This will hold them in place for
       -   Warning: Adding too much heat will distort the bacteria. The slide should be warm, not hot!
Staining the Bacteria
   9. Add enough Methylene Blue stain to cover the bacteria on the slide. Allow the dye to remain for 1-2
   10. Wash the excess stain off the slide with a little distilled water.
   11. Take a small piece of paper towel and blot off the excess stain (do not rub!).
   12. Place the slide under the microscope.
Viewing the Bacteria
   13. Place the microscope under the lowest power magnification.
   14. Using the course adjustment (large) knob, focus the slide until it is clear.
   15. Change to medium power magnification.
   16. Use both the course and fine (small) adjustment knobs to focus the slide.
   17. Change to high power magnification.
   18. Use only the fine (small) adjustment knob to focus the slide.
   19. Record your observations on the following pages.

Biology Teaching Resources                                        http://www.aurumscience.com             Page 1
Take a prepared bacteria slide and place it under the microscope. Focus the microscope under high power.
Scan through the slide and locate the three different shapes of bacteria. Draw a sample of bacteria from each
shape below.
Rod-shaped bacteria are named bacillus, sphere-shaped coccus, and spiral shaped spirilla. Label each of your
drawings above with the correct term to indicate shape.
Bacteria arranged in clusters are called “staphylo” while bacteria arranged in chains or pairs are called
“strepto”. Label each of your bacteria that show either of these patterns.

   Source: ______________                Source: ______________                   Source: ______________

   Source: ______________               Source: ______________                   Source: ______________

   Source: ______________               Source: ______________                    Source: ______________

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