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.


VIdeo demonstrations of Salmonella, Helicobacter, Leptospira and Proteus
movements or swarming are available in
Movies section.


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.
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.