This article describes a method for distinguishing motile and non-motile bacterial strains using a semisolid medium and a colorless redox dye. The experiment allows researchers to visualize bacterial motility through the diffusion of a red-colored product.
Begin with a culture plate containing a sample bacterial strain.
Using a sterilized inoculating needle, pick an isolated colony.
Under sterile conditions, puncture-inoculate this colony into a semisolid medium supplemented with a colorless redox dye. The semisolid medium restricts the passive diffusion of bacteria.
Prepare control tubes, a negative control with a non-motile bacterial strain lacking flagella, and a positive control with a highly motile, flagellated bacterial strain.
Incubate all inoculated tubes to support bacterial growth and motility.
During incubation, metabolically active bacteria reduce the colorless redox dye to an insoluble, red-colored product.
The motile bacteria proliferate and migrate through the semisolid medium using their flagella, creating a diffused red zone radiating outward into the surrounding medium.
Non-motile bacteria proliferate but do not migrate; the red zone remains confined to the puncture site.
This enables visual distinction of non-motile and motile bacterial strains.
Pick single colonies of bacteria from agar plates and inoculate them into both the semi-solid media by puncture using inoculating needles. Remember to include non-modal strains as negative controls and modal strains as positive controls.
Incubate the tubes at 37 degrees Celsius and observe the results after 24 to 48 hours of incubation. If only the puncture line is red, characterize the bacteria as non-modal.
If the red color spreads outward along the puncture line, characterize the bacteria as modal.
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