Virulence and the Mechanisms of Gene Regulation II

Question 1

List the steps required for V. cholerae to cause disease

Answer 1

1. Ingested via food or water
2. Survive passage through gastric acid barrier of the stomach
3. Colonize the upper small intestine
4. Produce and excrete toxin
5. Disseminate in a watery diarrhea

Question 2

List the 2 subunits of cholera toxin and describe their roles in producing diarrhea

Answer 2

A subunit (ctxA gene product): cleaved to active A1 subunit, activates G protein (Gsa) which activates AC -> cAMP -> PKA -> phosphorylates proteins involved in intestinal ion transport which causes water to leak into intestinal lumen (diarrhea)

B subunit (ctxB gene product): requried for secretion of A1 toxin out of bacteria cell, and the interaction with host cell surface receptor, GM1 glycoprotein

Question 3

Other cholera toxin virulence factors

Answer 3

Single polar flagellum
Toxin co-regulated pilus
Accessory colonization factors

tcp and acf genes, TCP-ACF element (pathogenicity island)

Question 4

Describe how ToxR and ToxT regulate the ToxR regulon

Answer 4

ToxR: acts as global virulence regulator, spans the cytoplasmic membrane
ToxR activates expression of tcp promoter and toxT transcription
ToxT is an activator that controls most ToxR regulon genes, including tcp operon. It autoregulates.

Question 5

Describe how temperature can regulate the ToxR regulon

Answer 5

Low temperature: toxRS is ON (ToxR and ToxS is synthesized and incorporated into the cytoplasmic membrane)
High temperature: toxRS is OFF. ToxR and ToxS not synthesized but old proteins still present in the membrane