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Bacterial Motility - (Mar/17/2013 )

Hi there,

I am trying to do some tests on bacterial motility using B. subtilis and E. coli as positive controls, M. luteus as negative control and one unknown bacterium. 16S data suggests the genus Corynebacterium. Thus, it should not move.

I conducted a wet mount test with a 25h old broth culture of these organisms but could not find one single moving E. coli cell (up to 1000x magnification). Regarding, B. subtilis, few cells were observable at 400x magnification.
The unknown bacterium did not exhibit an motion, but the test isn't valid because E. coli didn't move as well.

In another test I preapared test tubes containing ordinary LB medium (0.4% agar content). I inoculated the species in question with a needle and incubated until growth was good. B. subtilis grew at the surface only. E. coli showed enhanced growth were the needle was inserted.
My unknown bacteria exhibited little growth in the upper portion of the path of the needle. Additionally, there was a considerable and diffuse turbidity right below the surface of the medium.
I would rate this as motility, but Corynebacteria are non-motile.

What can I do? Has anyone tried to include MTT (maybe 0.5%) as indicator of growth?
Are there different, easy to perform tests for motility?

Thanks a lot!


Few if any lab strains of E. coli are motile. What strain were you trying to use as a positive control?


oh, I tested E. coli XL1-Blue MRF' (Stratagene) but I could not find any information on the strain's motility.
This week, I will spot a small volume of liquid inoculated broth on 0.1% agar containing plates, incubate and see what happens.


I'm not absolutely certain, but I strongly doubt that the cloning strains such as XL1 are motile. Something more like wild type, such as MG1655 would probably work well. If you have never compared the strains under a microscope, it is a revelation. Lab strains are very very sick, and look it.