Editing Leptospirosis (section)

===Bacteria===
[[File:Leptospira scanning micrograph.jpg|thumb|left|upright=1.3|alt=A scanning electron micrograph of several lepitospira bacteria on a filter | [[Scanning electron micrograph]] of a number of ''Leptospira'' sp. bacteria atop a 0.1 µm [[polycarbonate]] filter]]
Leptospirosis is caused by [[spirochaete]] bacteria that belong to the [[genus]] ''[[Leptospira]]'', which are [[Cellular respiration#Aerobic respiration|aerobic]],<ref name="Lane 2016"/> [[Screw thread#Handedness|right-handed]] [[Helix|helical]],<ref name=Picardeau2017/> and 6&nbsp;–20&nbsp;[[Micrometre|micrometer]]s long.<ref name="Karpagm2020"/> Like [[Gram-negative]] bacteria, ''Leptospira'' have an [[Bacterial outer membrane|outer membrane]] studded with [[lipopolysaccharide]] (LPS) on the surface, an [[Cell membrane|inner membrane]] and a layer of [[peptidoglycan]] cell wall. However, unlike Gram-negative bacteria, the peptidoglycan layer in ''Leptospira'' lies closer to the inner than the outer membrane. This results in a fluid outer membrane loosely associated with the cell wall.<ref name=Cameron2015>{{cite journal | vauthors = Cameron CE | title = Leptospiral structure, physiology, and metabolism | journal = Current Topics in Microbiology and Immunology | volume = 387 | pages = 21–41 | date = 2015 | pmid = 25388131 | doi = 10.1007/978-3-662-45059-8_3 | isbn = 978-3-662-45058-1 }}</ref> In addition, ''Leptospira'' have a [[flagellum]] located in the [[periplasm]], associated with corkscrew style movement.<ref name="Karpagm2020"/> [[Chemoreceptor]]s at the poles of the bacteria sense various substrates and change the direction of its movement.<ref name=Picardeau2017/> The bacteria are traditionally visualised using [[dark-field microscopy]] without staining.<ref name="Karpagm2020"/>

A total of 66&nbsp;species of ''Leptospira'' has been identified. Based on their genomic sequence, they are divided into two [[clade]]s and four subclades: P1, P2, S1, and S2.<ref name=Caimi2020>{{cite journal | vauthors = Caimi K, Ruybal P | title = Leptospira spp., a genus in the stage of diversity and genomic data expansion | journal = Infection, Genetics and Evolution | volume = 81 | pages = 104241 | date = February 2020 | pmid = 32061688 | doi = 10.1016/j.meegid.2020.104241 }}</ref> The 19 members of the P1 subclade include the 8 species that can cause severe disease in humans: ''[[Leptospira alexanderi|L. alexanderi]]'', ''[[Leptospira borgpetersenii|L. borgpetersenii]]'', ''[[Leptospira interrogans|L. interrogans]]'', ''[[Leptospira kirschneri|L. kirschneri]]'', ''L. mayottensis'', ''[[Leptospira noguchii|L. noguchii]]'', ''L. santarosai'', and ''[[Leptospira weilii|L. weilii]].''<ref name=Picardeau2017/><ref name=Caimi2020/> The P2 clade comprises 21 species that may cause mild disease in humans. The remaining 26 species comprise the S1 and S2 subclades, which include "saprophytes" known to consume decaying matter ([[saprotrophic nutrition]]).<ref name=Caimi2020/> Pathogenic ''Leptospira'' do not multiply in the environment. ''Leptospira'' require high humidity for survival but can remain alive in environments such as stagnant water or contaminated soil. The bacterium can be killed by temperatures of {{cvt|50|°C}} and can be inactivated by 70%&nbsp;[[ethanol]], 1%&nbsp;[[sodium hypochlorite]], [[formaldehyde]], detergents and acids.<ref name="Spickler 2013"/>

''Leptospira'' are also classified based on their [[Serotype|serovar]]. The diverse sugar composition of the lipopolysaccharide on the surface of the bacteria is responsible for the antigenic difference between serovars.<ref name=Picardeau2017/> Over 250&nbsp;pathogenic serovars of ''Leptospira'' are recognised, with closely related serovars gathered into over 26 pathogenic serogroups.<ref name="Lane 2016"/> Strains of different species of ''Leptospira'' may be members of the same serogroup because of [[horizontal gene transfer]] of LPS biosynthetic genes between different species.<ref name=Picardeau2017/>