Leptospira Pomona

''Leptospira'' () 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".

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 Haake et al. 1993">''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 Wolbach & Binger 1914">''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. hardjobovis''" Srinivas, Walker & Rippke 2013
* "''L. macculloughii''" Thibeaux et al. 2018

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.

Nutrition

''Leptospira'' are cultivated at 30 °C in Ellinghausen-McCullough-Johnson-Harris (EMJH) medium, which can be supplemented with 0.21% rabbit serum to enhance growth of fastidious strains. Growth of pathogenic ''Leptospira'' in an artificial nutrient environment such as EMJH becomes noticeable in 4–7 days; growth of saprophytic strains occur within 2–3 days. The minimal growth temperature of pathogenic species is 13–15 °C. Because the minimal growth temperature of the saprophytes is 5–10 °C, the ability of ''Leptospira'' to grow at 13 °C can be used to distinguish saprophytic from pathogenic ''Leptospira'' species. The optimal pH for growth of ''Leptospira'' is 7.2–7.6.

''Leptospira'' are aerobes whose major carbon and energy source during ''in vitro'' growth is long-chain fatty acids, which are metabolized by beta-oxidation. Fatty acids are provided in EMJH in the form of Tween. Fatty acid molecules are bound by albumin in EMJH and are released slowly into the medium to prevent its toxic accumulation.

Like most bacteria, ''Leptospira'' require iron for growth. ''L. interrogans'' and ''L. biflexa'' have the ability to acquire iron in different forms. A TonB-dependent receptor required for utilization of the ferrous form of the iron has been identified in ''L. biflexa'', and an ortholog of the receptor is encoded in the genome of ''L. interrogans''. ''L. interrogans'' can also obtain iron from heme, which is bound to most of the iron in the human body. The HbpA hemin-binding protein, which may be involved in the uptake of hemin, has been identified on the surface of ''L. interrogans'' Although other pathogenic species of ''Leptospira'' and ''L. biflexa'' lack HbpA, yet another hemin-binding protein, LipL41, may account for their ability to use hemin as a source of iron. Although they do not secrete siderophores, ''L. biflexa'' and ''L. interrogans'' may be capable of obtaining iron from siderophores secreted by other microorganisms.

Genome

The genome of pathogenic ''Leptospira'' consists of two chromosomes. The size of the genomes of ''L. interrogans'' serovars Copenhageni and Lai is approximately 4.6 Mb. However, the genome of ''L. borgpetersenii'' serovar Hardjo is only 3.9 Mb in size with a large number of pseudogenes, gene fragments, and insertion sequences relative to the genomes of ''L. interrogans.'' ''L. interrogans'' and ''L. borgpetersenii'' share 2708 genes from which 656 are pathogenic specific genes. The guanine plus cytosine (GC) content is between 35% and 41%. ''L. borgpetersenii'' serovar Hardjo is usually transmitted by direct exposure to infected tissues, whereas ''L. interrogans'' is often acquired from water or soil contaminated by the urine of carrier animals harboring ''Leptospira'' in their kidneys. The high number of defective genes and insertion sequences in ''L. borgpetersenii'' Hardjo together with the poor survival outside of the host and difference in transmission patterns compared to ''L. interrogans'' suggest that ''L. borgpetersenii'' is undergoing insertion-sequence mediated genomic decay, with ongoing loss of genes necessary for survival outside of the host animal.

Genotyping

Genome sequence determination several strains of ''Leptospira'' lead to the development of multilocus VNTR (Variable Number of Tandem Repeats) typing and multilocus sequence typing (MLST) for species level identification of pathogenic ''Leptospira'' species. Both methods hold the potential to replace the highly ambiguous serotyping method currently in vogue for leptospiral strain identification.

See also

* Leptospirosis
* List of bacteria genera
* List of bacterial orders

References

External links

*
''Leptospira'' page at Kenyon College MicrobeWiki.
*

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Spirochaetes
Bacteria genera