Spirochetes are slender, spiral‑shaped bacteria with flexible helical cells and unique axial filaments that provide a corkscrew‑like motility.
Explanation
The phylum Spirochaetes encompasses a diverse group of gram‑negative bacteria distinguished by their long, thin helical morphology (typically 0.1–0.3 µm wide and up to 250 µm long) and periplasmic flagella, also called axial filaments. These flagella originate at the ends of the cell and run between the inner and outer membranes; their rotation causes the entire cell to twist, allowing spirochetes to move through viscous environments such as mucus and connective tissues. Most spirochetes reproduce by transverse binary fission and have a flexible cell wall. They inhabit freshwater and marine sediments, decaying organic matter, and the gastrointestinal tracts of animals. Several genera are important pathogens: Treponema pallidum causes syphilis and yaws, Borrelia burgdorferi causes Lyme disease, and Leptospira interrogans causes leptospirosis. Other spirochetes, such as Spirochaeta species, are free‑living saprophytes that help decompose organic material. Diagnosis of spirochete infections often relies on dark‑field microscopy, serologic tests or nucleic acid amplification because these organisms are difficult to culture.
Major Genera and Features
- Treponema: Includes T. pallidum, the causative agent of syphilis, and T. denticola, a component of oral biofilms associated with periodontal disease.
- Borrelia: Species such as B. burgdorferi (Lyme disease) and B. recurrentis (louse‑borne relapsing fever); transmitted by ticks or lice.
- Leptospira: Thin, hook‑ended spirochetes that infect mammals and cause leptospirosis; acquired from contaminated water or soil.
- Spirochaeta: Free‑living anaerobes found in aquatic sediments and mud, important for nutrient cycling.
- Characteristic corkscrew motility enables spirochetes to penetrate host tissues and disseminate.
Spirochetes occupy diverse ecological niches and include notable human and veterinary pathogens. Understanding their unique structure and motility aids in diagnosing and managing spirochetal diseases.
Related Terms: Treponema, Borrelia, Leptospira, Axial Filament, Spiral Bacteria