Leptospira (from Ancient Greek λεπτός (leptós) 'fine, thin, narrow, etc.' and Latin spira 'coil') is a genus of spirochaete bacteria, including a small number of pathogenic and saprophytic species. Leptospira was first observed in 1907 in kidney tissue slices of a leptospirosis victim who was described as having died of "yellow fever". In 1917, Hideyo Noguchi named the genus Leptospira after witnessing it in the kidneys of American rats seemingly producing the same disease in Guinea pigs as in European rats.
Taxonomy Leptospira, together with the genera Leptonema and Turneria, is a member of the family Leptospiraceae. The genus Leptospira is divided into 20 species based on DNA hybridization studies. Pathogenic Leptospira
Leptospira alstonii Smythe et al. 2013 ["Leptospira alstoni" Haake et al. 1993] Leptospira interrogans (Stimson 1907) Wenyon 1926 emend. Faine and Stallman 1982 ["Spirochaeta interrogans" Stimson 1907; "Spirochaeta nodosa" Hubener & Reiter 1916; "Spirochaeta icterohaemorrhagiae" Inada et al. 1916; "Spirochaeta icterogenes" Uhlenhuth & Fromme 1916; "Leptospira icteroides" Noguchi 1919] Leptospira kirschneri Ramadass et al. 1992 Leptospira noguchii Yasuda et al. 1987 Leptospira alexanderi Brenner et al. 1999 Leptospira weilii Yasuda et al. 1987 Leptospira borgpetersenii Yasuda et al. 1987 Leptospira santarosai Yasuda et al. 1987 Leptospira kmetyi Slack et al. 2009 Leptospira mayottensis Bourhy et al. 2014 Intermediates or opportunistic Leptospira
Leptospira inadai Yasuda et al. 1987 Leptospira fainei Perolat et al. 1998 Leptospira broomii Levett et al. 2006 Leptospira licerasiae Matthias et al. 2009 Leptospira wolffii Slack et al. 2008 Non-pathogenic Leptospira
Leptospira biflexa (Wolbach and Binger 1914) Noguchi 1918 emend. Faine and Stallman 1982 ["Spirochaeta biflexa" Wolbach & Binger 1914] Leptospira idonii Saito et al. 2013 Leptospira meyeri Yasuda et al. 1987 Leptospira wolbachii Yasuda et al. 1987 Leptospira vanthielii Smythe et al. 2013 Leptospira terpstrae Smythe et al. 2013 Leptospira yanagawae Smythe et al. 2013 Members of Leptospira are also grouped into serovars according to their antigenic relatedness. There are currently over 200 recognized serovars. A few serovars are found in more than one species of Leptospira. At its 2002 meeting, the Committee on the Taxonomy of Leptospira of the International Union of Microbiological Societies approved the following nomenclature for serovars of Leptospira. Genus and species names are italicized as usual, with the serovar name not italicized and with an upper case first letter.
Genus species serovar Serovar_name For example:
Leptospira interrogans serovar Australis Leptospira biflexa serovar Patoc
Phylogeny The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN) and National Center for Biotechnology Information (NCBI).
Species incertae sedis:
"L. andamana" Tripathy, Evans & Hanson 1971 non Collier 1948 "L. brihuegai" Grune Loffler et al. 2015 L. cinconiae Hamond et al. 2025 L. gorisiae Hamond et al. 2025 "L. hardjobovis" Srinivas, Walker & Rippke 2013 L. iowaensis Hamond et al. 2025 "L. macculloughii" Thibeaux et al. 2018 L. mgodei Hamond et al. 2025 L. milleri Hamond et al. 2025
Morphology Although over 200 serotypes of Leptospira have been described, all members of the genus have similar morphology. Leptospira are 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. Because they are so thin, live Leptospira are best observed by darkfield microscopy. The bacteria have a number of degrees of freedom; when ready to proliferate via binary fission, the bacterium noticeably bends in the place of the future split.
Cellular structure Leptospira have 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 contains a variety of lipoproteins and transmembrane outer membrane proteins. As expected, the protein composition of the outer membrane differs when comparing Leptospira growing in artificial medium with Leptospira present in an infected animal. Several leptospiral outer membrane proteins have been shown to attach to the host extracellular matrix and to factor H. These proteins may be important for adhesion of Leptospira to host tissues and in resisting complement, respectively. 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. Consequently, immunity is serovar specific; current leptospiral vaccines, which consist of one or several serovars of Leptospira endemic in the population to be immunized, protect only against the serovars contained in the vaccine preparation. Leptospiral LPS has low endotoxin activity. An unusual feature of leptospiral LPS is that it activates host cells via TLR2 rather than TLR4. The unique structure of the lipid A portion of the LPS molecule may account for this observation. Finally, the LPS O antigen content of L. interrogans differs in an acutely infected versus a chronically infected animal. The role of O antigen changes in the establishment or maintenance of acute or chronic infection, if any, is unknown.
Habitat Leptospira, both pathogenic and saprophytic, can occupy diverse environments, habitats, and life cycles; these bacteria are found throughout the world, except in Antarctica. High humidity and neutral (6.9–7.4) pH are necessary for their survival in the environment, with stagnant water reservoirs—bogs, shallow lakes, ponds, puddles, etc.—being the natural habitat for the bacteria.
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