Regulation of Salmonella

Question 1

State why S. typhimurium infection of mice is a good experimental model for S. typhi infection of humans.

Answer 1

causes similar disease in mice (typhoid fever)

Question 2

Describe acid tolerance and its role in virulence.

Answer 2

bacteria must survive acidic conditions in the stomach and macrophage to survive and cause disease

• more than 50 acid shock proteins
• can be induced by acid, indirect environmental factors (heat, nutrient starvation, low ppO2, low iron concentration

Question 3

Describe the S. typhimurium process of invasion.

Answer 3

pathogen is ingested through contaminated food/water and after surviving acidic environments:

• colonization of the small intestine, preferably in Peyer’s patches of distal ileum
• bacterial-mediated endocytosis = attachment + ruffle formation and phagocytosis into M cells of intestinal epithelium
• macrophages in Peyer’s patches engulf pathogen and carry it to the RES
• express 40 bacterial proteins used to resist killing by macrophages
• systemic infection

Question 4

Describe the phoP-phoQ signal transduction pathway and its regulon.

Answer 4

1. phoQ = histidine kinase sensor that responds to low Mg concentration
2. phoP = response regulator
   => represses genes required for M entry (inv, spa) and macrophages (prg)
   => activates genes required for survival in macrophages (pag)

REGULON

1. inside M cell phagosome, bacteria notices low Mg => phoQ activates phoP
2. phoP activates pag genes (Pho-P Activated Genes)
3. phoP represses prg genes (Pho-P Repressed Genes) - since it is no longer necessary for the Type III secretory apparatus to invade into M cells and not yet needed for macrophage entry

Question 5

Define two-compartment signal transduction.

Answer 5

2CST - controls many virulence genes, including chemotaxis, capsule, toxin, and pili

1. sensor - histidine autokinase
   - membrane-bound receptor
   - autophosphorylates on histidine residue
   - uses ATP as phospho-donor
2. response regulator - aspartate autokinase
   - DNA-binding protein
   - autophosphorylates on aspartate residue
   - uses phosphate on sensor
   - can activate or repress
   - attached to DNA-binding domain

Question 6

Describe the disease caused by S. typhimurium in humans and mice.

Answer 6

typhoid fever (caused by S. typhi in humans)
normally, S. enterica infects human causing gastroenteritis; sometimes bacteremia, fever.

Question 7

Describe the role of pag genes in salmonella virulence.

Answer 7

• activated by pho-P
• virulence in mice
• survival in macrophages
• resistance to antimicrobial peptides (defensins) produced by macrophage

Question 8

Describe the role of low Mg concentration in salmonella virulence.

Answer 8

activates pho-Q sensor

Question 9

Describe the role of SPI1 in salmonella virulence.

Answer 9

Salmonella Pathogenicity Island 1

• mostly encodes type III secretory apparati required to export sip proteins (genes = inv, spa)
• sip proteins facilitate invasion into M cells via ruffling
• once inside, salmonella prevents fusion of phagolysosome
• travels through M cells inside phagosome
• second Type III apparatus facilitates entry into macrophages

Question 10

Describe the role of LPS in salmonella virulence.

Answer 10

type III secretory apparatus of salmonella embeds in the LPS to secrete sip proteins into M cell

Question 11

List the purposes for which salmonella uses Type III secretory apparati.

Answer 11

1. entrance into M cells

2. entry into macrophages