Spiral bacteria form the third major morphological category of prokaryotes, along with the rod-shaped bacilli and spherical cocci. Spiral bacteria can be sub-classified based on the number of twists per cell, cell thickness, cell flexibility, and motility.
- Members of the genus Spirillum.
- Campylobacter jejuni, a foodborne pathogen that causes campylobacteriosis.
- Helicobacter pylori, a cause of peptic ulcers that has been implicated in gastric cancer.
Spirochete (plural spirochetes) refers to very thin, elongate, flexible, spiral bacteria that are motile via endoflagella. Owing to their morphological properties, spirochetes are difficult to Gram-stain but may be visualized using dark field microscopy or Warthin–Starry stain. Examples include:
- Members of the family Spirochaetes.
- Leptospira species, which cause leptospirosis.
- Borrelia burgdorferi, a tick-borne bacterium that causes Lyme disease.
- Treponema pallidum, subspecies of which cause treponematoses.
Vibrio (plural vibrios) refers to Gram-negative, comma-shaped rods with a partial twist. One notable example includes:
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