A genus of the family Treponemataceae, thin coiled organisms, flagellated at the extremities, one or both of which are bent back like a hook. Both pathogenic and innocent forms have been isolated.

important pathogens causing Weil's disease or canicola fever

Leptospira is a genus of spirochaete bacteria, including a small number of pathogenic and saprophytic species. The first Leptospira to be described was L. interrogans in 1907 (as Spirochaeta interrogans) was isolated from kidney tissue slices of a Leptospirosis victim. Before genotypic methods such as DNA-DNA hyrbidisation and 16s rRNA gene sequencing, Leptospira were divided into either pathogenic species - L. interrogans sensu lato or saprophytic species - L. biflexa sensu lato using phenotypic tests such as growth at 13 °C or 30 °C and growth in the presence of 8-azaguanine.