Reg Vir Salm

Question 1

How does S. typhimurium invade once reaching the small intestine?

Answer 1

1. invading the M cells

a. attachment-change cytoskeleton of M-cell so that villi grow very large (ruffles) and they engulf the bacterium
- bacteria now in phagosome and want to avoid being brought to a lysosome

b. entry
- get into macrophages

• then M cell is destroyed
  2. entrance to reticuloendothelial system to bloodstream

Question 2

How does the pathogen facilitate entry into the M cells, survive phagosomes, survive macrophages?

Answer 2

type 3 secretory apparatus

found in all gram negative

Question 3

How does the pathogen facilitate entry into the M cells?

Answer 3

1. SPI 1 = pathogenicity island: inv and spa virulence genes
2. inv ands spa encode type 3 secretory system which exports sip proteins through bacterial cell surface to m cell
3. sip proteins facilitate invasion e.g. ruffling

Question 4

Why don’t lysosomes kill bacteria in phagosomes?

Answer 4

type 3 secretory apparatus

-secretes proteins into m cell cytosol inhibiting phagosome-lysosome fusion

Question 5

How does the pathogen facilitate entry into macrophages?

Answer 5

type 3 secretory system
1. SP1 pathogenicity island: (prgHIKL)

2. encode (EPs) which are exported through bacterial cell surface into the macrophage
3. facilitates phagocytosis by macrophage

Question 6

How does it survive the macrophage?

Answer 6

1. once inside represses genes necessary for entry (e.g. prgHIJK)
2. activates genes necessary to defeat macrophages defenses
3. samples environment for signals–>turns on certain regulons

Question 7

How does two component signal transduction work?

Answer 7

1. signal binds to the sensory domain in the periplasm
2. conformational change that crosses through the membrane and changes the structure of histidine kinase portion of the protein
3. changes causes the kinase to remove a phosphate group from the ATP and put it on its histidine group
4. now histine is a phospho donor for the response regulator–>transfers phosphate group to an aspartyl group
5. that activates the DNA binding domain on the other part of the response regulator
6. binds DNA that overlaps the promoter and represses transcription or activates

Question 8

What are some virulence factors that are controlled by 2 component signaling?

Answer 8

1. chemotaxis
2. pertussis toxin
3. capsule
4. phoPQ regulon

Question 9

How does the phoPQ regulon work?

Answer 9

1. Sensor PhoQ senses low Mg so it takes p off atp
2. PhoP phosphorylates itself
3. 2 types of PhoP regulated genes

a. repress genes prg–>required for entry into M cells and macrophages

b. activate genes pag
- depends on binding site
- required for survival in macrophages—ASPs and anti-defensins

Question 10

What is the evidence that PhoPQ system is required for virulence?

Answer 10

mutants are:

1. avirulent in mice
2. do not survive macrophages
3. are sensitive to low pH and defensins