Motility: Semi-Solid Motility Medium
Purpose The movement of bacteria is detected by use of a medium with low agar concentration. The medium is inoculated with an inoculating needle, incubated with other tubed media, and can be read without the need for a special stain and microscope.

Principle The lower agar concentration in the medium allows limited movement of motile bacteria from the area of the stab. Motility will be detectable as diffuse growth radiating from the stab line. A special dye, a tetrazolium salt (TTC) may be added to make the radiating growth more visible as the reddish diffuse area.

Additional Information The stab is performed with an inoculating needle, shown at right. Care must be taken to insert the needle straight in and to pull it straight out. If the needle "slices" the agar horizontally, it may be difficult to tell if the resulting bacterial growth is from motile bacterial, or is just growth along a wide stab line.

MOTILITY TEST
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Organism Test Result
1. Pseudomonas aeruginosa（铜绿假单胞菌）：Motile
2. Staphylococcus aureus：Non-motile
3. Bacillus subtilis：Motile

Reading the Test: An organism that is motile will grow out into the surrounding medium-it will migrate out away from the stab line. In the second tube (S. aureus) it is easy to see that there is growth at the stab line and the surrounding medium is clear (no growth there = non-motile). In the other tubes (B. subtilis and P. aeruginosa) the medium is slightly more turbid when compared to the second tube, indicating growth throughout the medium.