RANK: Genus

TAXONOMY: cellular organisms -> Bacteria -> Spirochaetes -> Spirochaetia -> Leptospiraceae -> Leptospira


eptospira are long, thin, flexible rods, 0.1 μm in diameter and 6–12 μm in length, with a regular right-handed helical coiling pattern (Carleton et al., 1979). These bacteria are unicellular but may be observed as dividing pairs or short chains of three or more cells in actively growing cultures. Resting stages are not known, but long term survival in water, with the appearance of aggregates has been described (Trueba et al., 2004). Spherically shaped cells form under unfavorable growth conditions. Bacteria stain as Gram-negative. Due to the small diameter of these bacteria, unstained cells are not visible by bright-field microscopy. Dark-field or phase-contrast microscopy is required for visualization of unstained cells. These are highly motile aerobic or microaerophilic bacteria. Optimum growth temperature is 28–30°C, with a generation time of 6–16 h, although many primary pathogenic isolates may grow slower. Chemoorganotrophic bacteria that consume long-chain fatty acids and alcohols as primary carbon and energy sources, and carry out respiration with oxygen as the terminal electron acceptor. Optimal growth occurs in semi-solid (0.1–0.2%) agar media. Growth on 1–2% solid agar results in the formation of clear to turbid surface or subsurface colonies. Colony formation is enhanced by the addition of pyruvate. Oxidase, catalase, and/or peroxidase-positive. Some strains are β-hemolytic. Some strains are pathogenic for humans and animals, while other strains are saprophytic and found in freshwater and marine environments. The genus Leptospira forms a deep unique branch of spirochetes, separate from other genera based on comparison of 16S rRNA gene sequences. Species are differentiated by DNA–DNA relative reassociation analysis and by unique sequence polymorphisms in 16S rRNA.DNA G+C content (mol%): 35–43.Type species: Leptospira interrogans