Differential Media:
Motility Medium

In our lab, determining the presence or absence of flagella is done by "indirect" methods, as we detect whether or not motility is evident under growth conditions made as favorable as possible for the organisms.

With the wet mount, an actively-growing, "young" broth culture is required for observation. Motile organisms are usually easily seen as they move among each other in separate directions.

We can also utilize tubes of Motility Medium wherein only motile bacteria can move away from the line of inoculation in the low (0.5% or less) concentration of agar; descendants of cells which have migrated throughout the medium show up as evidenced by turbidity (cloudiness) in the medium. One advantage of using Motility Medium is that a culture of any age can be used for inoculation – as long as it is pure and viable! After incubation the tubes are held up against a relatively dark background in a brightly-lighted environment. Ignoring growth at the surface of the medium and also between the medium and the wall of the tube, one should be able to distinguish motile from non-motile organisms such as in the photo at right. Generally, one should confirm microscopically any negative reaction seen in Motility Medium.

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Department of Bacteriology, U.W.-Madison