Visualization of Bacterial Motility Using Redox Dye–Supplemented Semisolid Medium

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 n