Vibrio Flashcards
(26 cards)
What are the main strains of vibrio?
Cholerae, parahaemolyticus and vulnificus
Characteristics of vibrio
Gram negative rod
Facultative anaerobe
Sensitive to heat
Acid sensitive but also tolerant to pH>11
How is vibrio distributed?
Water
Fish, shellfish
Isolated from GI tract and faeces of infected individuals
Symptoms of cholerae
Mild diarrhoea to severe illness (cholera)
Hypotension and dehydration cause collapse and organ failure
Replace lost fluids to treat
What is cholera caused by?
Non-invasive infection and toxin production
Where are cholera outbreaks common?
Haiti and Yemen
What serotypes of cholerae cause cholera?
O1 and O139
How does cholerae cause cholera?
Requires Cholera enterotoxin (CTX)
Cells bind to enterocytes (small intestine) for toxins to act on
Structure of CTX
1 A subunit which is A1 and A2 linked by an SS bond with 5 B subunits
How does CTX cause infection?
B subunits bind to ganglioside receptor on cell surface. Toxin enters, traffics to endosomes then to TGN and ER. A1 released to activate cyclase. CAMP accumulates, inhibiting Cl- and Na+ absorption and stimulating Cl- secretion.
Why does movement of electrolytes matter?
Changes osmotic balance and flow of water, overwhelming large intestine
What are the virulence factors of CTX?
Vibrio pathogenicity island (VPI)
Toxin coregulated pilus
Accessory colonisation factor
Transmembrane protein
What are the colonisation factors of CTX?
LPS of O1 is involved in mucosal adhesion
Polysaccharide capsule of O139 mediates adhesion to epithelial cells
What is the dose of CTX required to cause illness?
10^6cfu/g
Characteristics of parahaemolyticus
Halophilic (salt)
Marine waters
Uncooked fish
More heat sensitive than cholerae
Tolerates pH 5
What is the dose of parahaemolyticus required for illness?
10^5-7 with symptoms occurring after 9-24h
What are the symptoms of parahaemolyticus?
Diarrhoea
Cramps
Nausea
Vomiting
Mucous and blood in stools
Symptoms last 3-5d
What is the Ka toxin?
Kanagawa toxin found in parahaemolyticus
How does the Ka toxin cause infection?
Produces TDH
TDH induces Cl- secretion and targets ganglioside GT1b
TDH uses Ca2 as signal
Similar effect to CTX
What is TDH?
Thermostable direct haemolysin which induces permeability of capillaries
Characteristics of vulnificus
Warm coastal waters (30C)
Salt requiring
Oysters
16-48h incubation
Symptoms of vulnificus
Speticemia (fever, chills, nausea)
Diarrhoea
Abdominal pain
Why is infection of vulnificus rare?
Protected by oestrogen and killed by cooking
Structure of vulnificus
Fimbriae attachment
Polysaccharide capsule
LPS acts as endotoxin causing circulatory collapse
