Transcript 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 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:
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 non chemotactic CCW-biased state improved infection of new human hosts