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Biology and Biotechnology department
 A large number of bacteria are motile.
 Most possess one or more flagella on their
surface that allow them to swim.
 The pattern of flagellation is an important
feature in identification of motile
bacteria.
 The figure illustrates the commonly observed
arrangements of flagella.
 Polar flagella occur at one or both ends of
the bacterium (Vibrio cholerae and some
species of Pseudomonas).
 They may be single or in tufts.
 Peritrichous flagella are distributed
around the surface of the organism
(many Proteus species).
 Most motile bacteria move in a straight
line for a brief time, then turn and randomly
change directions before swimming again.
 Many flagellated bacteria can move toward
useful chemicals and away from harmful
ones.
 This ability to control movement in response to
chemical stimuli is termed chemotaxis.
 Chemotactic bacteria contain receptors in
the cell membrane that bind to certain
chemicals and cause the basal body to direct
either a run or tumble (or forward and reverse
directions).
 Hanging Drop Technique:-
 This method is commonly used to view
living
organisms
for
the
rapid
determination of motility.
 The hanging drop is prepared by suspending
a fluid sample from a coverslip over a
depression well in a specially designed
microscope slide.
 Wet mounts can be used for the same
purpose, however, wet mounts tend to
dehydrate rapidly.
 Hanging drops, on the other hand, are
sealed within the depression and retain their
liquid for longer periods of time.
 In both methods, the living specimen is
unstained.
 For best results, reduce the amount of
light passing through the specimen.
Procedure:1. Place a drop of the bacterial culture
(optimally from a young broth culture) in the
middle of a cover slip.
2. Place a thin line of petroleum jelly around the
edge of the cover slide.
3. Turn the depression slide upside-down
(depressed area facing down) and gently touch the
cover slide. The jelly holds the cover slip to the
slide and also keeps the suspension from drying
out.
4. Now flip the entire microscope slide/cover
slip combination over. It should look like the
diagram below.
Positive control: Proteus vulgaris.
Negative controle: Staph. Epidermidis.
 Motility Agar : Motile bacteria require liquid to move.
 Thus bacteria can propel themselves in broth
or across the surface of a wet agar plate.
 They will not however move when embedded
in 1.5% agar, the minimum concentration
 found in most agar media.
 Semisolid agar has a reduced agar
concentration (0.4 %) that allows flagellated
bacteria to migrate from the site of inoculation.
 Semisolid media are prepared in tubes and
are inoculated through most of their
length by stabbing
 with a needle.
 Thus after 48 hours of incubation, growth
of a motile organism will be observed as a
turbid region extending from the stab.
 No motile bacteria will only grow along the
stab line.
Positive control: Proteus vulgaris.
Negative controle: Staph. Epidermidis
Procedure
1. Using aseptic techniques, inoculate the
tube by stabbing with the needle to
approximately three-quarters of its
depth. Be careful to bring the needle into
the center of the medium and not to touch
the side of the tube.
2. Incubate at room temperature for 48 hours.
3. Examine for growth.
Interpretation :
(A)Pattern of growth of a motile organism. The
entire medium is turbid with the growth of
the organism, which has moved away from
the stab line.
(B) Pattern of growth of a nonmotile organism.
Only the stab line is turbid with growth.
Note: Semi solid media with tetrazolium
chloride (color indicator)