Leptospira spp

Leptospira is a genus of spirochaete bacteria, including a small number of pathogenic and saprophytic species. Although over 200 serotypes of Leptospira have been described, all members of the genus have similar morphology. Leptospira is spiral-shaped bacteria that are 6-20 μm long and 0.1 μm in diameter with a wavelength of about 0.5 μm. One or both ends of the spirochete are usually hooked. Leptospira has a Gram-negative like cell envelope consisting of a cytoplasmic and outer membrane. However, the peptidoglycan layer is associated with the cytoplasmic rather than the outer membrane, an arrangement that is unique to spirochetes. The two flagella of Leptospira extend from the cytoplasmic membrane at the ends of the bacterium into the periplasmic space and are necessary for the motility of Leptospira. The outer membrane of Leptospira, like those of most other Gram-negative bacteria, contains lipopolysaccharide (LPS). Differences in the highly immunogenic LPS structure account for the numerous serovars of Leptospira.