Virulence II Flashcards
List the 4 stresses that V. cholerae must survive to cause disease.
- ingested via contaminated food or water
- survive low pH of the stomach
- have adhesive/invasive properties in order to colonize small intestine
- produce and excrete toxin
- disseminate watery diarrhea
List the 2 subunits of cholera toxin and their roles in producing diarrhea.
2 Alpha subunit
- encoded for by ctxA gene
- cleaved to reveal active A1 subunit
- catalyzes ADP-ribosylation of Gas => activates AC => cAMP => PKA
- phosphorylation of proteins involved in intestinal ion transport => water leaks into lumen
- severe watery diarrhea
5 Beta subunit
- encoded for by ctxB gene
- required for A1 toxin to be secreted out of the bacterial cell
- 5 subunits act as scaffold to hold A2-A1
- required for interaction with host cell surface receptor GM1 glycoprotein
List 3 other virulence factors, their roles, and the genes that encode them.
- TCP-ACF => motility and adhesion
- ToxR => toxR => global regulator (TM)
- ToxS => toxS => environmental sensor (TM)
Describe how ToxR and ToxT regulated the ToxR regulon.
- toxR and toxS form an operon
- transcription is regulated by temperature
Describe how temperature can regulate the ToxR regulon.
low temperature = operon is ON
=> toxRS transcribed, synthesized and localized to cytoplasmic membrane
high temperature in upper GI = operon is OFF
=> no further toxRS transcribed; but proteins already on the membrane remain there (basal level)
high temperature in intestines = signals ToxS
- communicates with ToxR
- cytoplasmic domain of ToxR binds to TCP-ACF element
- activates TCP-ACF
ADP-ribosylation of the Gas protein results in the activation of what host enzyme?
- adenylate cyclase
Describe the TCP-ACF element.
- TCP (toxin co-regulated pilus) encodes for flagellum to allow motility into colonization site
- ACF (accessory colonization factor) encodes for adhesins/invasins to colonize the site
- mutations in these genes decrease virulence
- TCP-ACF element is a large pathogenicity island where both genes are located
How does transduction play a role in disseminating cholera?
V. cholerae requires transduction by phage carrying ctx genes to produce toxin
Describe the function of ToxR, ToxS, ToxT.
- ToxS sense the environment and activates ToxR in the high temperatures of the intestine
- ToxR is a transcription factor that activates TCP-ACF-ToxT element
- ToxT autoregulates by regulating the ToxR operon and the CTX operon
How does ToxT autoregulate?
- part of tcp domain
- activated by ToxR
- ToxT is an activator that controls ToxR regulon
- thus autoregulates since tcp is part of ToxR regulon
- activates many other operons, including ctx
If the toxT gene were deleted, which of the following genes would have their transcription affected? not affected?
- toxT
- toxS
- tcp
- acf
- ctxB
- toxT, ctxB, tcp-acf
- toxS unaffected
Describe Vibrio cholerae.
- highly motile
- uniflagellated
- gram (-)
- curved rod
- extracellular pathogen
- causes cholera (life-threatening diarrheal disease that can rapidly attain epidemic proportions; transmitted through unsanitary food)
Describe the role of the flagellum in V. cholerae colonization.
- required for virulence
- regulatory network alternates expression of motility genes and toxin genes
==> first, motility to get to colonization site. THEN toxin genes to cause disease
