Advanced Biology

Document Sample
Advanced Biology Powered By Docstoc
					Demonstration of Motility

Two convenient methods are available for demonstration of motility. In one of these the cells may
be shown to move by direct microscopic examination of a young culture. In the other, the use is
made of the ability of a motile organism to show diffuse growth from a stab inoculation in a
semisolid nutrient agar deep. We usually use SIM media and 5.4% agar.


    1.       Young nutrient broth cultures (12-18 hours) of Bacillus subtilis and Escherichia coli.
    2.       Depression slides
    3.       Clean glass cover slips
    4.       Vaseline and toothpicks
    5.       Microscope


             1.              Prepare a hanging drop slide of each culture using aseptic
                             techniques, and examine for motility. To prepare the slide, first place
                             a small spot of Veseline on each corner of a cover galls (a). Place a
                             small drop of culture on the cover glass (b). Invert the depression
                             slide over the small drop of culture so that the depression covers the
                             drop and cause the spots of Vaseline to stick to the depression slide.
                             Press down gently to form a firm seal (c). Invert the slide so that the
                             cover glass is on top (d).
             2.              Examine the preparation first with the low power lens and then with
                             the high power dry lens (do not us oil immersion lens). After
                             locating the drop with the 10x (yellow) lens, move the slide so that
                             the edge of the drop is in the exact center of the field, then swing the
                             40x (blue) lens down. Obtain a clear image of the edge of the drop
                             before attempting to locate the individual bacterial cells. After the
                             cells have been distinguished, study carefully the evidence of
                             motion. Distinguish between true motility or movement and
                             Brownian movement (vibration of molecules against the cells)
                             Record your observations.
                                                           Describe the motility if observed
Bacillus subtillis


    1.       If you were studying the motility of bacteria causing typhoid fever, which method
             would you use?
    2.       Why are young cultures used for the examination of motility?
    3.       What is Brownian movement?