Download V. Cholerae

Vibrio cholerae:
• 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
Virulence factors
• cholera toxin:
 ribosylating enterotoxin
 secreted AB5 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:
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:
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 nonchemotactic CCW-biased state
 improved infection of new human hosts
Thank you for your attention