Vibrio cholera

Question 1

Cholera

Answer 1

Disease caused by vibrio cholera. It causes severe watery diarrhoea. Causing people to loose over 20 L of water a day. This causes severe dehydration, low circulating blood and other issues related to mineral loss.
It is injested via contaminated water. The infectious dose is 10^4 to 10^8 but stool from infected has 10^9 per ml.

Question 2

Vibrio cholera cycle

Answer 2

Toxigenic strains cycle between living in aquatic environments and living in hosts.
In the aquatic environment, planktonic vibrio float around in the water. While Aggregate vibrio clump together in biofilms and adhere to chitin on zooplankton, insect eggs, exoskeletons or detritus.
In hosts, the Vibrio needs to adhere to the mucosal lining of the epithelial cells of the intestine. Here they aggregate and form biofilms, until they want to leave, and leave with the stool.

Question 3

Vibrio Cholera acquisition of viral genes

Answer 3

1. First they need to be able to attach to the epitheliim, using a type IV pilus.
2. Then a phage infects cells with a type IV pilus with a gene encoding cholera toxin. Using T4 pilus as a receptor.
3. Acquisition of the SXT mobile genetic elements, which carries resistance to many antibiotics.

Question 4

TCP Toxin co-regulated pilus

Answer 4

This is an adhesin that allows bacteria to attach to host cells. It functions via a grapple hook mechanism, extending the pilus, attaching and then retracting to pull the cell to the attachment site.
The pilus is built up of subunits called PilA (pilin). PilA prepilin is first processed by PilD to form pilin. PilA is added to the pilus by PilC activated by pilB, extending the pilus. The pilus has a PilC1 adhesin tip. Once the tip binds this creates tension causing a conformational change where PilB is replaced with PilT which gets PilC to remove pilin for retraction.

Question 5

Choleratoxin (CT)

Answer 5

This is an AB5 protein. The A1 subunit and A2 subunits have an exposed peptide cut, only keeping them attached to eachother by disulfide bonds. The CT binds to the GM1 receptor, causing endocytosis of the toxin. This is brought to the ER, where the A1 detached from the protein. A1 subunit then is released into the cytoplasm where it binds a G protein, causing it to activate Adenalyl cyclase. Which produces cAMP. cAMP activates ion pumps, which pump ions out of the epithelial cells into the intestine. This causes a change in the osmotic gradient, causing water to leave the cells.

Question 6

Flagellar motitility

Answer 6

Allows the bacteria to move and attach to the sites. It also allows penetration of the mucus layer.

Question 7

GbpA

Answer 7

This is an adhesin that allows for attachment to chitin in water and attachment to mucin in hosts.
When the bacteria wants to leave, Hap proteins cleave GbpA.

Question 8

Mucinase

Answer 8

Breaksdown the mucus, allowing for CT GM1 binding.

Question 9

Biofilm in aquatic environments

Answer 9

Biofilms form on chitinous surfaces. Cholera can use chitin as a carbon source. Flagellar motility and pilus allow for surface attachment. They produce biofilm ECM proteins such as polysaccharide and matrix proteins.

Question 10

Biofilm in host

Answer 10

Biofilms allow bacteria to survive shear force and attach to intestines. Biofilm dispersal allows for release into the environment. Hap degrades GbpA.

Question 11

Protein secretion systems

Answer 11

Move proteins from inside to outside the cell. Needed to move proteins across the outer membrane. Type 3 4 and 6 secrete proteins directly into hosts.

Question 12

Vibrio cholera secretion

Answer 12

Vibrio cholera secretes proteins in to the extracellular space via T2SS. It secretes proteins via a piston system.

Question 13

Vibrio cholera injection

Answer 13

Vibrio cholera need to get rid of competing commensal bacteria for space. They use the T6SS to secrete antibacterial toxins into competing bacteria.

Question 14

V. cholera Virulence regulation

Answer 14

Virulence is regulated via quorum sensing. At low density, LuxPQ and CqsS are not bound by autoinducers. This allows LuxU and LuxO to be active in their phosphorylated forms. The signal cascade activates the transcription of a sRNA which promotes AphA production while suppressing HapR expression. AphA promotes TcpPH which together with ToxRS, activates ToxT which promotes TCP and CT production. AphA also pormotes biofilm production.
When there is high cell density, LuxPQ and CqsS are bound by the autoinducer and they dephosphorylate LuxU, causing LuxO to be depshorylated. The sRNA is no longer expressed, and Aph1 is no longer promoted, while HapR is free to be expressed. HapR suppresses virulence genes and promotes Hap protease production. Hap degrades adhesins, allowing escape.

c-di-GMP promotes biofilm formation.
cAMP activates HapR.