Regulation of Salmonella Virulence

Question 1

Why is S. typhimurium useful to study in mice even though it is not the cause of typhoid fever in humans?

Answer 1

In mice, it mimics the effects that S. typhi has in humans and essentially produces the same result.

Question 2

How does acid tolerance in salmonella contribute to virulence?

Answer 2

Acid tolerance allows for the survival in the stomach, which allows the bacteria to reach the intestines where they can enact their pathogenicity.

Question 3

How is acid tolerance generated in salmonella?

Answer 3

The acid shock proteins

Question 4

Is salmonella intracellular or extracellular?

Answer 4

Intracellular

Question 5

What is SP1?

Answer 5

Many of the genes required for invasion are located on a 40-kB pathogenicity island called SPI1 (SALMONELLA PATHOGENICITY ISLAND).

Question 6

What are some genes that are encoded from SP1?

Answer 6

inv and spa

Question 7

What do inv and spa code for?

Answer 7

Type III secretory protein that is used to export Sip proteins into cells

Question 8

How does M cell entry occur?

Answer 8

Type III secretory protein is used to export Sip proteins into the M cell that cause ruffling of the M cell and leads to phagocytosis of the salmonella

Question 9

Within the phagosome, how does the salmonella survive?

Answer 9

It inhibits fusion of the phagosome with the lysosome

Question 10

How does the salmonella enter macrophages after entering a phagosome in the M cell?

Answer 10

The lack of phagosome-lysosome fusion allows the bacterial cell to transit through the M cell to interact with a macrophage where it uses a second Type III secretory system to facilitate macrophage phagocytosis

Question 11

What does prgHIJK encode?

Answer 11

The Type III secretory protein used for entry into macrophages

Question 12

What are the parts of the Two Component Signal Transduction?

Answer 12

Sensor - His Autokinase

Response Regulator - Asp DNA Binding Protein

Question 13

How does the 2CST system function?

Answer 13

Membrane bound His sensor will have ATP donate Pi on activation which will lead to Pi of the Asp response regulator leading to DNA binding to either activate or repress genes.

Question 14

What is the PhoQP system of salmonella?

Answer 14

It is a 2CST system used for invasion and survival in the macrophage to signal when the cell has reached the inside of a macrophage

Question 15

What is PhoQ?

Answer 15

PhoQ is a membrane-bound histidine kinase sensor that senses low Mg2+ concentrations

Question 16

What is PhoP

Answer 16

PhoP is its cognate response regulator that functions as a DNA-binding protein. Phospho-PhoP represses genes required for invasion into M cells and macrophages

Question 17

What are prg genes?

Answer 17

PhoP-repressed genes

prg - genes for invasion of M cells

Question 18

What are pag genes?

Answer 18

PhoP-activated genes

pag - genes for survival in the macrophage

Question 19

What happens to the regulation of prg and pag when PhoQ senses that salmonella has reached the inside of a macrophage?

Answer 19

Phospho-PhoP represses genes required for invasion into M cells and macrophages (prg). Simultaneously, it activates genes required for survival in macrophage (pag).

Question 20

Is PhoQP required for virulence?

Answer 20

Yes.

Because null mutants of PhoP are attenuated.

Question 21

A mutation in phoP that destroys its function will affect all of following except:
A. spa transcription
B. Phosphorylation of PhoP 
C. Phosphorylation of PhoQ 
D. Secretion of Sip proteins

Answer 21

C. Phosphorylation of PhoQ