L21 virulence and gene reg II

Question 1

Vibrio cholera

Answer 1

highly motile, uniflagellated, gram-negative curved rod.

extracellular pathogen

Question 2

to cause disease vibrio cholera must

Answer 2

be ingested
 survive passage through the gastric acid barrier of the stomach
colonize the upper small intestine
produce & excrete toxin
 disseminate in a watery diarrhea

Question 3

cholera toxin

Answer 3

main virulence factor- even a small dose reults in full-blown diarrhea

mutants w/o toxin genes are much less virulent

2 subunits A and B

Question 4

CTX phage

Answer 4

contains the ctxA and ctxB genes

Question 5

A subunit

Answer 5

ctxA gene product
cleaved to yield active A1 subunit
through a G protein cascade causes unregulated ion transport which causes water to leak into the intestinal lumen= sever watery diarrhea

Question 6

B subunits

Answer 6

there are 5 of them
they are required for secretion of A1 toxin out of the bacterial cell and for interaction with host cell surface receptor GM1 glycoprotein

Question 7

process of G-protein cascade

Answer 7

G-protein activates AC which activates cAMP activating PKA which activates ion transporters. ions and water leave the cell= diahrrea

Question 8

flagellum

Answer 8

signal polar flagellum
not active when cholera toxin gene is being expressed
strains lacking flagellum are less virulent

motility used to reach site of colonization
motility genes turned off
colonization and toxigenic genes turned on

Question 9

TCP

Answer 9

TCP (toxin colonization pilus)

part of the ToxR regulon

Question 10

ACF

Answer 10

ACF (accessory colonization factors)

part of the ToxR regulon

Question 11

TCP-ACF element

Answer 11

large pathogenicity island containing tcp and acf genes

Question 12

mutations in tcp or acf

Answer 12

reduce colonization

Question 13

ToxR

Answer 13

a protein that acts as the global virulence regulator the product of the toxR gene spans the cytoplasmic membrane

Question 14

ToxS

Answer 14

a protein that acts as the environmental sensor also spans the cytoplasmic membrane

Question 15

ToxRS regulations

Answer 15

toxR and toxS form an operon, toxRS transcription is regulated by temperature

at low temperature (outside the host) the toxRS operon is ON
ToxR and ToxS are synthesized and incorporated into the membrane

at high temps (host’s upper GI tract) the operon is OFF
ToxR and ToxS are not synthesized but old proteins still present in the membrante

at high temps (intestines)
ToxS receives a signal unique to the intestinal environment
communicates with ToxR
cytoplasmic domain of ToxR binds TCP-ACF element DNA
TCP-ACF transcription is activated (including toxT)

Question 16

toxT regulation

Answer 16

activation of the ToxRS operon activates toxT transcription then ToxT autoregulates to increase its own transcription and transcription of most ToxR regulon genes

= lots of ToxT made

Question 17

vibrio cholera virulence requires products of genes located

Answer 17

within the chromosome
  - toxRS operon
a pathogenicity island incorporated within the chromosome
  - TCP-ACF element including toxT
a temperate or lysogenic bacteriophage
  - the CTX phage carrying ctxAB