Cholera

Question 1

Vibrio cholerae

Answer 1

Facultative anaerobe
Gram negative
Does not produce spores
Can enter a viable but non-culturable state
Two serogroups O1 and O139 cause cholera

Question 2

Vibrio cholerae in the environment

Answer 2

Found in coastal waters and estuaries
Free-living or in association with zooplankton (stuck to side as biofilm) and shellfish
Seasonality of outbreaks follow blooms of zooplankton

Question 3

V. cholerae and zooplankton

Answer 3

Attached to chitin of zooplankton
Can secrete chitinase for nutrients
Metabolically active at high acidic environment without losing viability/virulence

Question 4

V. cholerae genome

Answer 4

Chromosome I contains housekeeping genes. VPI gene (attachment pilus) and CTX (enterotoxin).
VPI and CTX inserted by a virus

Chromosome II contains integron island

Question 5

V. cholerae virulence factors

Answer 5

ACF (accessory colonisation factor). Involved in chemotaxis (intestinal colonisation).
Flagella (adhesion or biofilm formation)
Auto inducer 2 (AI-2) facilitates interspecies communication. LuxPQ receptor responds to AI-2
T6SS. Antibacterial and anti-eukaryotic activities
Cholera A5B toxin

Question 6

Quorum sensing

Answer 6

Secretion and detection of signalling molecules (autoinducers)
Expression of virulence factors and formation of biofilms at low density
Repression at high cell density and motility switched back on

Question 7

V. cholerae colonisation

Answer 7

After ingestion, V. cholerae uses motility and mucinases to penetrate mucus gel
GbpA (binding protein) to colonise small intestine epithelium
Expresses vieA, a phosphodiesterase which hydrolyses cyclic di-GMP
Represses chitin-binding mannose-sensitive haemagglutinin pilus

Question 8

Escape response

Answer 8

Prepares for transmission to another host
Genes for di-GMP synthesis and nutrient scavenging systems
Repression of genes for chemotaxis and ToxR regulon
Motile but non-chemotactic state

Question 9

Exposure to chitin

Answer 9

V. cholerae induces genes involved in adherence and catabolism of chitin (ChiS regulon)
Genetic competenec (TfoX regulon)
Biofilm formation mediated by induction of Vps regulon

Question 10

Active but non-culturable state

Answer 10

If V. cholerae not ingested by host or attached to chitin
Adaptation to nutrient-poor conditions
Phosphate and nitrogen starvation genes (phoB and glnB-1)
Repression of translation machinery genes

Question 11

V. cholerae infection

Answer 11

Secretes enterotoxin which binds intestinal cells
Chloride channels activated
Release of electrolytes and bicarbonates
Fluid hypersecretion out of intestine
Diarrhoea and dehydration (main effect on host)

Question 12

Action of cholera toxin

Answer 12

5B:1A toxin binds GM1 receptor and taken in by endocytosis
Phagosome transported to ER
A1 subunit detached from B and exported to cytoplasm
Affects G-protein that regulates adenylate cyclase
cAMP levels rise and active ion transport systems

Question 13

Routes of infection

Answer 13

Faecal-oral
Person to person infection is indirect
Can be carried by houseflies and other insects

Question 14

Cholera treatment

Answer 14

Main treatment is oral rehydration (or intravenous)
Antibiotics (tetracycline)
Serological anti-vibrio antibodies
Antitoxin antibodies