Leptospires are finely coiled, thin, motile, and obligate aerobes. Their flagella help them to burrow deep into infected tissues.
The leptospires belong to the genus Leptospira, the family Leptospiraceae, and the order Spirochaetales. The nomencla-ture and taxonomy of the Leptospira has undergone a lot of revisions, making review of the literature often confusing.
Traditionally, the genus Leptospira has been grouped by serological properties and by their pathogenicity into two spe-cies: the pathogenic Leptospira interrogans and nonpathogenic Leptospira biflexa. On the basis of shared antigens, these specieswere further divided into serogroups, serovars, and strains. Pathogenic species, L. interrogans currently includes more than 250 serovars. However, the classification is not consistent with recent classification based on nucleic acid analysis. The current classification based on nucleic acid analysis divides L. interrogans and L. biflexa complex into 12 species. These species are further subdivided into serogroups, serovars, and strains on the basis of microscopic agglutination tests (MAT):
· L. interrogans complex includes pathogenic leptospires thatcause leptospirosis
· L. biflexa consists of nonpathogenic leptospires and includesmore than 63 serovars. L. biflexa is so called because of its double curved structure (Biflexa: twice bend). These are mostly free-living saprophytes found in moist environmental areas but are not associated with disease in humans and animals.