spirokeetit

Spirochetes, commonly known in Finnish as spirokeetit, are a phylum of slender, helical bacteria notable for their long, flexible bodies and distinctive mode of movement. They are typically described as Gram-negative, though Gram staining is often unreliable because of their thin, coiled cells and their periplasmic flagella, which lie between the cytoplasmic and outer membranes. The flagella, or axial filaments, wrap around the cell and rotate to produce a corkscrew propulsion that enables movement through viscous environments such as tissue and mucus. Size varies from about 0.2–0.5 μm in width and up to 20 μm in length.

Major genera include Treponema, Borrelia, and Leptospira. Other genera such as Spirochaeta and Brachyspira are also classified within the group. Members inhabit a range of niches, from animal hosts to environmental reservoirs, and several species are pathogens of humans and animals. Many spirochetes are difficult to culture under standard laboratory conditions and require specialized media or host cells for growth.

Pathogenic spirochetes are associated with several notable diseases. Treponema pallidum causes syphilis; Borrelia burgdorferi (and related species) cause Lyme borreliosis; Borrelia recurrentis causes relapsing fever; and Leptospira interrogans causes leptospirosis. Transmission routes include sexual contact, tick or louse bites, and exposure to contaminated water or soil.

Diagnosis relies on serology, molecular methods such as PCR, and, for some species, direct visualization in clinical samples by dark-field or fluorescence microscopy; culture is often slow or unsuccessful. Treatment typically uses antibiotics such as penicillin G, with doxycycline as an alternative for certain infections. Vaccines exist for some animal infections, but there is no widely used human vaccine for most spirochete diseases.

Spirochetes have complex genomes and express surface lipoproteins that mediate host interactions, making them a focus of study in microbiology and infectious disease.