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
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
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?