7.6: Observation of Bacterial Motility

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Animation showing spirochetes using motility to enter a blood vessel.

To detect bacterial motility, we can use any of the following three methods: 1) direct observation by means of special-purpose microscopes (phase-contrast and dark-field), 2) motility media, and, indirectly, 3) flagella staining.

1. Direct observation of motility using special-purpose microscopes.

a. Phase-contrast microscopy

A phase-contrast microscope uses special phase-contrast objectives and a condenser assembly to control illumination and give an optical effect of direct staining. The special optics will convert slight variations in specimen thickness into corresponding visible variation in brightness. Thus, the bacterium and its structures appear darker than the background.

b. Dark-field microscopy

A dark-field microscope uses a special condenser to direct light away from the objective lens. However, bacteria (or other objects) lying in the transparent medium will scatter light so that it enters the objective. This gives the optical effect of an indirect stain. The organism will appear bright against the dark background. Dark field microscopy is especially valuable in observing the very thin spirochetes. (See Fig. \(\PageIndex{1}\)).

Photomicrograph of <i>Borrelia burgdorferi</i> as seen using darkfield microscopy. — Figure \(\PageIndex{1}\): **Darkfield Microscope Photomicrograph of the Spirochete Borrelia burgdorferi**. Note Gram-positive bacilli with clear endospores. (Â© Jeffrey Nelson, author. Licensed for use, ASM MicrobeLibrary.)

Videos of bacterial motility

Video of motile Escherichia coli with fluorescent labeled-flagella #1 Courtesy of Dr. Howard C. Berg from the Roland Institute at Harvard.

Video of motile Escherichia coli with fluorescent labeled-flagella #2 Courtesy of Dr. Howard C. Berg from the Roland Institute at Harvard.

Video of swimming Escherichia coli as seen with phase contrast microscopy Courtesy of Dr. Howard C. Berg from the Roland Institute at Harvard.

Video of tethered Escherichia coli showing that the bacterial flagella rotate Courtesy of Dr. Howard C. Berg from the Roland Institute at Harvard.

Video of swarming motility of Escherichia coli Courtesy of Dr. Howard C. Berg from the Roland Institute at Harvard.

Video of motile Pseudomonas from YouTube.

Video of motile Rhodobacter spheroides with fluorescent labeled-flagella Courtesy of Dr. Howard C. Berg from the Roland Institute at Harvard.

Video of motile Borrelia bergdorferi, the spirochete that causes Lyme disease. From You Tube, courtesy of CytoVivo.

Video of motile Borrelia bergdorferi, the spirochete that causes Lyme disease.

Contributors and Attributions

Dr. Gary Kaiser (COMMUNITY COLLEGE OF BALTIMORE COUNTY, CATONSVILLE CAMPUS)