Bacterial Motility
The ability of bacteria to move independently using metabolic energy
depends on the use of different appendages to propel like flagella. The most
accurate way to visualize the moving  bacteria is the microscopy and
'hanging drop method' is a commonly used microscopic technique: a drop of
fresh liquid culture is suspended on a clean glass slide, a coverslip is
added, and the culture is observed under microscope.


Semisolid media like MIU or SIM allow the visualisation of bacterial motility
by medium stabbing method. Motility is positive if the entire medium became
opaque (semisolid state of the medium permits the bacteria moving). Result
is negative if the culture grows only on the stabbing line.


Other types of movement occurring on solid surfaces include twitching,
gliding and sliding, which are all independent of flagella. Twitching motility is
used to move over surfaces and results from type IV pili activity which extend
from the cell's exterior, bind to surrounding solid substrates and retract,
pulling the cell forwards similarly to the action of a grappling hook.


Video demonstrations of Salmonella, Helicobacter, Leptospira, Proteus and
Bacillus movements or swarming are available in
Movies section.
Twitching motility: migrating Moraxella colonies on
Sheep Blood Agar
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Left: non-motile bacteria - growth on stabbing line.
Right: motile bacteria - uniform medium turbidity.
Demonstration of Proteus swarming: waves of
growing bacteria starting from a central point.