Med Micro 12 - Cholera Flashcards
Why does cholera turn off biofilm formation when it has quorum sensing?
Its means of transmission is via diarhea so it needs to be able to be dislodged etc.
What reservoir is there for cholera?
Found in the water - lots of nutrients in unclean water
Cholera and phage
When infected with phage, it expresses toxin. WIthout phage, no toxin. Binds via pili
Quorum sensing in cholera
forms biofilm automatically. Quorum sensing required to turn it off.
Toxin co-regulated pili
If pili aren’t there, toxin isn’t expressed. Phage binds to pili, so cannot have toxin without pili
Access to clean water
Most diseases in developing world (80%) is caused by dirty water
Global warming?
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
Structures of digestive system
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)
Bacterial gastroenteritis
Inflammation of stomach/intestines due to various bacteria. Contaminated food/water/bad conditions. Nausea, vomiting, etc., dysentery (blood in feces)
Vibrio genus
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.
Two types of cholera
Classical and El Tor. Both have 2 chromosomes.
Bacteriophage
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.
Why would this phage retain the cholera toxin gene?
Phage does not require the gene. Toxin gives it ability to infect and therefore reproduce alongside cholera. An example of microbial evolution
Pathogenicity Islands and cholera
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
What is a pathogenciity island?
Several genes for virulence factors close together. Often have secretory systems included. Makes sense to make secretion and system at same time.
How do you know there is a pathogenicity island?
Look at GC ratio. Classic.
Type 3 secretion system
Associated with specific virulence factors. Expressed at same time as virulence factor.
Black death
Pathogenicity island taken up made a normally benign soil bacteria into a super powerful pathogen overnight.
Why were we not able to cope well with black death then?
The immune system has developed a lot since then.
Why are some bacteria able to evolve more quickly than others?
Naturally competent can take up DNA easier. (Growth rate). (DNA repair mechanisms). Receptors for bacteriophages that can integrate DNA
Just because one bacteria does not have the ability to become naturally competent does this mean they don’t evolve?
No. Phage receptors. Replication errors.
Cholera infection
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)
Cholera treatment
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
Why are Ab and chemotherapeutics not effective?
The toxin is the problem. Besides, infections are self-limiting. You just need rehydration.
AB toxin
Cl gets secreted, then water and electrolytes, from cells and then the blood
Why are the number of deaths from cholera increasing?
Not enough clean water because larger and denser population, easier spread. Global warming too.
Cholera colonization of small intestine - what virulence factors?
Adhesins (pili), neuraminidase/protease (degrade mucus), motility, chemotaxis, toxin, biofilm
Diagram of genetic regulation
Low cell density – LuxO is expressed, inhibits HapR; High cell density – LuxO is repressed, HapR is expressed. HapR inhibits pili and toxin.
Pili
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
Neuraminidase/Protease
Digest mucus layer and GMI gangliosides generating the toxin binding receptor. It generates its own receptor!
Cholera toxin
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
Under normal circumstances what would be responsible for continued activation of adenylyl cyclase?
Ligand binding for as long as it is needed.
Cholera toxin mechanism
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..
Diagram of cholera toxin function
Picture
Summary
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
Discuss how V cholerae displays both mulfifactorial and multidimesional aspects in the pathogenesis of cholera
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)
Discuss V cholerae and microbial evolution
Received a pathogenicity island containing virulence factors. Phage provides lateral gene transfer b/w strains of cholera
How do we enter the convalescence stage of cholera?
bacteria get washed out by diarrhea. This is what we mean by self-limiting.
