Med Micro 12 - Cholera

Question 1

Why does cholera turn off biofilm formation when it has quorum sensing?

Answer 1

Its means of transmission is via diarhea so it needs to be able to be dislodged etc.

Question 2

What reservoir is there for cholera?

Answer 2

Found in the water - lots of nutrients in unclean water

Question 3

Cholera and phage

Answer 3

When infected with phage, it expresses toxin. WIthout phage, no toxin. Binds via pili

Question 4

Quorum sensing in cholera

Answer 4

forms biofilm automatically. Quorum sensing required to turn it off.

Question 5

Toxin co-regulated pili

Answer 5

If pili aren’t there, toxin isn’t expressed. Phage binds to pili, so cannot have toxin without pili

Question 6

Access to clean water

Answer 6

Most diseases in developing world (80%) is caused by dirty water

Question 7

Global warming?

Answer 7

An increase in temperature by 1ºC six weeks before the rain season increases the number of people affected by cholera by 4.9%. Increases their growth

Question 8

Structures of digestive system

Answer 8

Stomach is major defence against most ingested bacteria. Low pH inhibits gene expression and metabolic pathways. Parenteral route? Through teeth if extracted etc bacteria will access bloodstream. They will form biofilm on implants (in heart, mouth, etc)

Question 9

Bacterial gastroenteritis

Answer 9

Inflammation of stomach/intestines due to various bacteria. Contaminated food/water/bad conditions. Nausea, vomiting, etc., dysentery (blood in feces)

Question 10

Vibrio genus

Answer 10

Vibrios are one of the most common organisms in surface waters of the world; occur in both marine and freshwater habitats and in associations with aquatic animals, there are many different types, both parasitic and mutualistic.

Question 11

Two types of cholera

Answer 11

Classical and El Tor. Both have 2 chromosomes.

Question 12

Bacteriophage

Answer 12

Cholera toxin encoded by filamentous phage (which can transduce the ctx gene into other cholera strains which must express co-regulated pili). The released phages specifically attach to the bacterium and enter it. Vigorous viral multiplication results in the production of large amounts of toxin causing severe diarrhea.

Question 13

Why would this phage retain the cholera toxin gene?

Answer 13

Phage does not require the gene. Toxin gives it ability to infect and therefore reproduce alongside cholera. An example of microbial evolution

Question 14

Pathogenicity Islands and cholera

Answer 14

Pathogenicity island codes for several virulence factors. Acquired from elsewhere. toxin-coregulated pilus (TCP) is part of pathogenicity island which is found in pathogenic cholera strains. An example of microbial evolution

Question 15

What is a pathogenciity island?

Answer 15

Several genes for virulence factors close together. Often have secretory systems included. Makes sense to make secretion and system at same time.

Question 16

How do you know there is a pathogenicity island?

Answer 16

Look at GC ratio. Classic.

Question 17

Type 3 secretion system

Answer 17

Associated with specific virulence factors. Expressed at same time as virulence factor.

Question 18

Black death

Answer 18

Pathogenicity island taken up made a normally benign soil bacteria into a super powerful pathogen overnight.

Question 19

Why were we not able to cope well with black death then?

Answer 19

The immune system has developed a lot since then.

Question 20

Why are some bacteria able to evolve more quickly than others?

Answer 20

Naturally competent can take up DNA easier. (Growth rate). (DNA repair mechanisms). Receptors for bacteriophages that can integrate DNA

Question 21

Just because one bacteria does not have the ability to become naturally competent does this mean they don’t evolve?

Answer 21

No. Phage receptors. Replication errors.

Question 22

Cholera infection

Answer 22

Cholera toxin’s (AB toxin) action on the mucosal epithelium is responsible for the characteristic diarrhea; usually death in 1.5-several days; extreme cases, it is one of the most rapidly fatal illnesses known (death within 2-3 hours)

Question 23

Cholera treatment

Answer 23

Easy enough to treat with rehydration. It is a problem in developing world because you cannot get clean water. Most antibiotics and chemotherapeutic agents have no value in cholera therapy

Question 24

Why are Ab and chemotherapeutics not effective?

Answer 24

The toxin is the problem. Besides, infections are self-limiting. You just need rehydration.

Question 25

AB toxin

Answer 25

Cl gets secreted, then water and electrolytes, from cells and then the blood

Question 26

Why are the number of deaths from cholera increasing?

Answer 26

Not enough clean water because larger and denser population, easier spread. Global warming too.

Question 27

Cholera colonization of small intestine - what virulence factors?

Answer 27

Adhesins (pili), neuraminidase/protease (degrade mucus), motility, chemotaxis, toxin, biofilm

Question 28

Diagram of genetic regulation

Answer 28

Low cell density – LuxO is expressed, inhibits HapR; High cell density – LuxO is repressed, HapR is expressed. HapR inhibits pili and toxin.

Question 29

Pili

Answer 29

Tcp (toxin coregulated pili) most important; Expression of these pilin genes is coregulated with expression of the cholera toxin genes. Tcp pili share sequence similarity with Pseudomonas and Neisseria . Twitching, important in microcolony formation

Question 30

Neuraminidase/Protease

Answer 30

Digest mucus layer and GMI gangliosides generating the toxin binding receptor. It generates its own receptor!

Question 31

Cholera toxin

Answer 31

AB toxin activates the adenylate cyclase enzyme in mucosa, increased levels of intracellular cAMP, which causes the secretion of Cl-, then H2O, Na+, K+, and HCO3- follow into the small intestine. Draws water etc out of blood

Question 32

Under normal circumstances what would be responsible for continued activation of adenylyl cyclase?

Answer 32

Ligand binding for as long as it is needed.

Question 33

Cholera toxin mechanism

Answer 33

B binds. A is endocytosed, goes through trans side of golgi, then to cytosol. A part inhibits the shut off of adenylyl cyclase by transfering ADP-ribose from NAD to AC-Gs which activates it, Gi cannot hydrolyze GTP from it, so lots of cAMP produced, Cl- secreted, etc..

Question 34

Diagram of cholera toxin function

Answer 34

Picture

Question 35

Summary

Answer 35

Low cell density: biofilm; protease, neuraminidase, ctx; chemotaxis and motility; HAP repressed. High density: Quorum sensing inhibits biofilm; inhibit pili and toxin, express HAP protease; diarrhea leads to transmission

Question 36

Discuss how V cholerae displays both mulfifactorial and multidimesional aspects in the pathogenesis of cholera

Answer 36

More than one virulence factor (toxin and pili, protease, etc.), and regulation (biofilm, pili and toxin turned off when quorum is reached so it will be washed out)

Question 37

Discuss V cholerae and microbial evolution

Answer 37

Received a pathogenicity island containing virulence factors. Phage provides lateral gene transfer b/w strains of cholera

Question 38

How do we enter the convalescence stage of cholera?

Answer 38

bacteria get washed out by diarrhea. This is what we mean by self-limiting.