gram-negative cause of severe diarrheal disease around 120,000 death per annum 200 known serogroups  cholera associated only with two serogroups (O1 and O139)  O1 divided in two serotypes (Inaba and Ogawa) and further in two biotypes (classical and El Tor) humans are the only known vertebrate host, infection by ingestion V. cholerae is not particular ph-resistant, so infection seems to require high dose (about a million bacteria) small intestine is the main site of infection idea that chemotaxis needed to find colonization niche and virulence factor expression Vibrio cholerae:

Virulence factors cholera toxin:  ribosylating enterotoxin  secreted AB 5 subunit toxin, B unit binds to epithelia cells, A units enter cells via endocytosis  permanent ribosylation of G proteins resulting in constitutive cAMP production.  leads to secretion of H2O, Na+, K+, Cl-, and HCO3- into the lumen  responsible for watery diarrhea (rice-water stool) toxin co-regulated pilus (TCP)  required for colonization in human and animal models  pili are believed to mediate microcolony formation gene expression is tightly regulated, no expression in extra-intestinal growth

Lifecycle of pathogenic Vibrio cholerae:

can shed ten trillion bacteria per day these bacteria are highly motile Shed bacteria can be ingested by other humans or settle into enviromental-reservoir stage Cholera is natural inhabitant of freshwater, brackish and coastal-water habitats It can exist in a free-living form or associated with hosts like zooplankton or form biofilms

Flagellar-based motility:

Different kinds of flagellation in bacteria Peritrichous flagella are found for example in E.coli, monotrichous flagellum in V. Cholerae covered by extension of the outer membrane can achieve around 100,000 revolution per minute (sodium-motive force) other forms of motility: twitching motility and gliding motility

Chemotactic in V. cholerae and other bacteria: in flagellar motility chemotaxis is achieved by modulating direction, speed… best understood in E.coli

Chemotactic in V. cholerae and other bacteria: in flagellar motility chemotaxis is achieved by modulating direction, speed… best understood in E.coli signal reception by methyl-acccepting chemotaxis proteins MCP cluster at cell pole ligand occupancy is communicated to flagella can respond to change of a few molecules

Chemotactic in V. cholerae and other bacteria: in flagellar motility chemotaxis is achieved by modulating direction, speed… best understood in E.coli V. cholerae has many chemotaxis paralogues organized in three operons but only operon 2 important in vitro strains with single or combined mutations in the paralogues retain full virulence in mouse model speculated that operon 1 and 3 regulate flagellum-independent motility

The role of chemotaxis in virulence: motility and chemotaxis ranges from being crucial to being dispensable Shigella species that are non-motile but highly infectious invasive enteric bacteria might nor require motility for infection (translocation through M cells) non-invasive pathogens (H. pylori) require chemotaxis to stay within the mucus layer chemotaxis inhibits V. cholera colonization non-chemotactic mutants showed 10-fold increased infectivity advantage is specific to host small intestine

Intestine colonization by V. cholerae: wild-type mainly colonize in the lower half of the small intestine  bile is a possible attractant non-chemotactic mutants are found in the whole small intestine  less specific – greater surface area to colonize only CCW-biased flagellar mutants show out-competition phenotype these mutants swim in straight runs direction is random but the covered distance is enough in regard to diameter of small intestine lumen

Intestine colonization by V. cholerae: wild-type colonize at the base of villi proposed that there are antimicrobial substances present that kill bacteria  like definsins released from Paneth cells non-chemotactic mutants are mainly found in the mucus layer and the luminal side of the villi reasons for wild-type to be attracted to the base of the villi: signal of max. expression of cholera toxin better protection from peristalsis might be crucial in humans

Motility and V. cholerae virulence: to determine the role of motility it must be separated from adherence effects of the flagella  comparison of fla - and fla + mot - mutants no differences in V. cholerae but motility itself seems to be important in some organism motility is inhibited by virulence gene expression - not in V. cholerae bacteria in rice-water stool are highly motile  switched back on before exit the host speculated that rice-water V. cholerae might be in a transiently non- chemotactic CCW-biased state  improved infection of new human hosts

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