1. Signal Transduction & Virulence
Low [Mg++]
PhoQ
pag
(+)
PhoP P
(-)
DBD
prg

2. SALMONELLOSIS gastroenteritis and enteric fever
caused by nontyphoid Salmonella
increased significantly in the last decade
(0.8 to 3.7 million cases per yr)

3. Salmonella enterica (serovar Typhimurium) = S. typhimurium
INFECTIOUS AGENT
Salmonella enterica (serovar Typhimurium)
= S. typhimurium
intracellular pathogen
usually results in self-limiting gastroenteritis
sometimes results in
bacteremia, fever & other complications

4. a severe systemic disease of humans causes a similar disease in mice
Typhoid fever
a severe systemic disease of humans
caused by S. typhi
Research Model
S. typhimurium
causes a similar disease in mice

5. S. typhimurium to cause disease must
survive and propagate in a wide range of tissues
to survive and propagate,
S. typhimurium must
circumvent or hijack
host immune system
uses macrophages to enter the bloodstream
HOW?

6. Ingestion of contaminated food or water But also, acidic macrophage
Infection
Ingestion of contaminated food or water
must survive
lysozyme in saliva
acid stomach
alkaline bile salts
anaerobiosis
high osmolarity
low iron content
But also, acidic macrophage
HOW?

7. INVASION after surviving the trip, cells colonize the small intestine,
invading the M cells
(specialized epithelial cells that
take up luminal antigens)
Invasion occurs by Bacterial-mediated Endocytosis
Two-steps
i) attachment
ii) entry

8. Attachment
LUMEN
vili
M cell

9. Ruffle formation & phagocytosis
phagosome
ruffles
LUMEN
vili
epithelial
cell
M cell
macrophages

10. Entry
LUMEN
phagosome
macrophages

11. M cell destroyed
Entrance to
Reticuloendothelial
System
to bloodstream

12. How does the pathogen Facilitate entry into M cells?
Survival in phagosomes?
Survival in macrophages
1. Type III secretory apparatus
2. Type III secretory apparatus
3. Type III secretory apparatus
Signal transduction and gene expression

13. Phenotypic effects of Type III secretion mechanisms on host cells

14. facilitate entry into M cells?
How does the pathogen
facilitate entry into M cells?
Type 3 secretory apparatus
phagosome
ruffles
LUMEN
M cell

15. How does the pathogen facilitate entry into M cells?
Sip
Sip
inside M cell
Sip
Sip
Sip
LPS
outer membrane
Type III
Apparatus
periplasm
cytoplasmic membrane
SPI 1
large pathogenicity island
includes inv & spa
virulence genes
encode a Type III secretory system
which exports Sip proteins
through bacterial cell surface
into the host M cell
Sip proteins facilitate invasion
e.g. ruffling
cytoplasm }
invA spa
sip (exported)
SPI 1

16. kill bacteria in phagosomes?
Why don’t lysosomes
kill bacteria in phagosomes?
phagosome
Type 3 secretory apparatus
Secretes proteins into the M cell cytosol
Inhibiting phagosome-lysosome fusion
LUMEN

17. } How does the pathogen facilitate entry into macrophages?
Inside macrophage EP EP EP
LPS
outer membrane
Type III
Apparatus
periplasm
cytoplasmic membrane
cytoplasm }
another Type III secretory system (prgHIKL)
exports proteins (EPs)
through bacterial cell surface into the macrophage
Facilitates phagocytosis by macrophage
prgHIKL also encoded by SPI 1
prgHIJK
EPs
SPI 1

18. Survive in macrophages?
How does the pathogen
Survive in macrophages?
macrophages

19. How does the pathogen survive the adverse environment
once inside the macrophage,
S. typhimurium
represses genes necessary for entry
(e.g., prgHIJK)
&
activates genes necessary to defeat
macrophage defenses
How does the pathogen survive
the adverse environment
of the macrophage?

20. How does the pathogen “sense” that is inside the macrophage?

21. (transcription factor) phosphodonor = phosphorylated sensor
Two-component Signal Transduction
SENSOR
(receptor)
Histidine autokinase
phosphodonor = ATP
RESPONSE REGULATOR
(transcription factor)
Aspartate autokinase
phosphodonor = phosphorylated sensor

22. Two-component Signal Transduction
An example

23. = ATP P P transcription repression ADP sensor phospho-donor RNAP RR
DBD

24. sensor P
ADP
= ATP
phospho-donor
transcription
activation
RNAP RR
DBD

25. Very Short List of VIRULENCE FACTORS CONTROLLED BY
2-COMPONENT SIGNALING
CHEMOTAXIS - Escherichia coli & others
PERTUSSIS TOXIN - Bordetella pertussis
CAPSULE - Pseudomonas aeruginosa
PhoPQ regulon - Salmonella typhimurium

26. { = ATP P P PhoP prg (PhoP-repressed genes) ADP sensor phospho-donor
RNAP P RR
DBD {
PhoP
prg
(PhoP-repressed
genes)

27. (PhoP-activated genes)
sensor P
ADP
= ATP
phospho-donor
RNAP P RR
DBD {
PhoP
pag
(PhoP-activated genes)

28. signal transduction pathway PhoP = response regulator
PhoPQ
a two-component
signal transduction pathway
PhoQ = sensor
PhoP = response regulator
represses prg
activates pag
Low [Mg++]
PhoQ
pag
(+) P
PhoP
(-)
DBD
prg

29. prg (PhoP-repressed genes) pag (PhoP-activated genes)
required for
entry into
M cells & macrophages
(inv, spa, sip, prgHIJK)
pag (PhoP-activated genes)
survival in macrophages
ASPs & anti-defensins
[defensins are antimicrobial peptides produced by macrophages]

30. Evidence that PhoPQ system is required for virulence
mutants
i) are avirulent in mice
ii) do not survive macrophages
iii) are sensitive to
low pH
&
defensins