Bacteriology - cellular invasion Flashcards Preview

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Flashcards in Bacteriology - cellular invasion Deck (201):
1

Chlamydia binding

Probably many receptors. cell-surface exposed PDI may be bound by EB and have an enzymatic role in entry.

2

Chlamydial entry - actin rearrangements.

Requires Rac1 dep remodelling.

3

Chlamydial Rac1 remodelling

Injection of Tarp, phosphorylation --> recruitment of Sos and Vav (Rac1 GEFs) and Abi-1 --> WAVE complex activity --> Arp2/3.
Possible role for Ct694.

4

Chlamydial transition EB --> RB

EB outer proteins are cross-linked. Disulphide bonds are reduced on internalisation --> nucleoid decondensation --> transcription.

5

Chlamydial effector secretion system.

T3SS

6

Chlamydial effectors inserting into inclusion membrane are called...

Inc

7

Inc-recruited proteins

Rab1, 4, 11; recycling endosome and Golgi related Rab GTPases.
Dynein for transport to perinuclear regions.

8

Chlamydial inclusion body formation and nutrient delivery.

Needs lipids (sphingolipids, cholesterol) for development.
a) Golgi fragmentation
b) Multivesicular bodies
c?) Non-classical routes e.g. lipid droplets

9

Inhibition of host cell death: Chlamydia.

Early block, late induction

10

Chlamydia: early block of apoptosis.

Stabilises inhibitor of apoptosis proteins.
Sequesters pro-apoptotic BAD.
Degrades BH3 only proteins. --> less Bax activation --> less cyt c release.

11

Intracellular bacteria - host cell death.

Inhibition - early chlamydia
Induction - late chlamydia, salmonella, shigella

12

Chlamydia - general

obligate intracellular pathogen.

13

Intracellular bacteria rapidly escaping cell cytoplasm.

Shigella, Listeria

14

Intracellular bacteria remaining withing the membrane bound vesicle.

Salmonella, Legionella pneumophila, Brucella abortus or Chlamydia spp

15

Chlamydial target cells

Epithelial cells.

16

Chlamydial entry sites

Occur at lipid microdomains.

17

Bacteria using raft-dependent entry pathways.

Shigella flexneri, Fim H-expressing E. coli, Brucella spp. and Chlamydia spp.
May confer special properties to the early inclusion/vesicle.

18

Chlamydial entry overview.

Adhesins, lipid microdomains, actin cytoskeleton reorganisation.

19

Intracellular bacteria uptake

Zipper, trigger, other mechanisms, phagocytosis.

20

Intracellular survival

Bacterial developmental transition.
Stay in the vacuole?
Manipulating the host cell

21

Manipulating the host cell

Bacteria containing compartment interacting with other compartments.
Altering host cell death
Inhibiting immune response.

22

Exiting the host cell

Host cell death.
Exocytosis.
Intracellular spread.

23

Host endocytotic pathway

Endocytosis/macropinocytosis --> EE --> late endosomes and acidification --> lysosomes.

24

Zipper mechanism

Express surface proteins.

25

Trigger mechanism

Inject effector proteins.

26

Result of chlamydial transition to RB.

New effectors by T3SS system.
Some insert into membrane - Incs.

27

Chlamydia inhibiting immune response

Block nuclear translocation of NFkB.
Increase NFkB degradation.

28

Inhibiting the immune response - mechanisms

Alter TLR binding
Alter NFkB
Alter cytokine mRNAs
Avoid autophagy.

29

Chlamydial cell escape

Transition from RB to EB and exit by host cell death.

30

Endocytic pathway. Endocytosis-->early endosomes.

Decrease inclusion of normal endocytic ones.
Use bacterial proteins to recruit Rabs (Chlamydia).

31

Endocytic pathway. EE --> LE.

GTPase Rab5 does this. Recruits EEA1

32

Endocytic pathway. LE --> lysosomes, mechanism

Calcium fluxes.

33

Endocytic pathway. LE --> lysosomes, mechanism; calcium fluxes.

Important in signalling maturation of lysosome. Ca++ influences calmodulin recruits Rab5 recruits PI3P
-->EEA1
--> v-ATPases
--> hydrolases.

34

Inhibiting Ca++ induced lysosomal fusion.

Unknown mechanism by cord factor. (TB).
Inhibited by phosphatidylinositol derivatives e.g. LAM.

35

LAM full name.

lipoarabinomannan

36

LAM action

Inhibits Ca++ mediated fusion; reduces development to a late endosome or acidification even if just on beads. With mannose caps inhibits recruitment of EEA1 as well.

37

Lysosomal conditions

Acidification via v-ATPase.
Acid hydrolases
Phagolysosomal oxidative burst.

38

Ways to survive acidification of lysosome.

TB: stop this.
Survive and divert hydrolases: Coxiella.

39

Coxiella survival of lysosome

Coxiella (passively continues down endosomal pathway until this point). Even just 5 minutes after internalisation it acidifies. Delayed acquisition of lysosomal enzymes such as cathepsin D.

40

How many acid hydrolases are there?

About 60.

41

Which bacteria decrease presence of acid hydrolases?

TB (none)
Salmonelal (very few, and few of their receptor, mannose-6-phosphate).

42

Mechanism of oxidative cell burst.

NADPH oxidase complex recruited by Rac (a Rho GTPase). Electron transfer occurs from NADPH to FAD to oxygen to make superoxide anions of various sorts.

43

Inhibiting oxidative cell burst

Superoxide dismutase by many pathogens.
Interfere with assembly/recruitment of NADPH oxidase.

44

Interfering with NADPH oxidase.

A phagocytophilum
Listeria
Salmonella

45

General intracellular replication points

Use conditions to stimulate replication.
Accumulation of nutrients.
Space limitations
Alteration of vacuolar structure.
Salmonella-induced filaments.

46

Space limitations in vacuole.

Acquisition of more lipids expands envelope of organelle.

47

Chlamydia Golgi fragmentation

Necessary for nutrient delivery.
Cleavage of Golgin-84 by CPAF gives access to sphingolipids by Golgi fragmentation. Formation of mini-stacks around the inclusion, triggers re-differentiation into EBs.

48

Interacting with other compartments - necessary for replication: delivery of nutrients.

Chlamydial Golgi-fragmentation.
Host proteins to facilitate accumulation.

49

Altering vacuolar structure for replication.

• Recruitment of mitochondria and ribosomes causes formation of ER like structure in which bacteria replicate (Legionella). Effector proteins via Dot/Icm.

50

Recruiting autophagy pathway for replication?

Coxiella. Autophagy vesicles loaded with membranes.

51

Role of salmonella induced filaments?

Formation of filaments probably causes intracellular survival and replication of bacteria but not fully understood.
Possible role for egress.

52

Bacteria using the zipper mechanism.

Listeria, Yersinia.

53

Listeria - general bacterial invasion mechanisms

Actin rearrangements.
Microtubule dependent.
Intermediate filaments and septins contribute to invasion efficiency.

54

Bacteria using intermediate filaments and septins

E. Coli, Salmonella, Listeria, Shigella.

55

Listeria binding proteins

Internalins InlA and InlB anchored to membrane via LPXTG or GW motifs. Leucine rich repeats critical for function. Determine cell tropism and host range.

56

InlA - binding.

Binds E-Cadherin, species specific. Has leucine rich curve which grips around it.
Listeria.

57

E-Cadherin clustering (bound by InlA)

Zipper, Listeria.
Binds catenins on cytoplasmic side. Interact with actin. Arp2/3 activated.

58

InlB - binding

Binds MET via LRR repeats which curve and grip. Listeria.

59

MET clustering due to InlB binding.

Mimics hepatocyte growth factor, but downstream recruits ABI and WAVE, and dynamin and cortactin.

60

Escaping the vacuole: Listeria.

Uses LLO and PLCs

61

LLO

Secreted by Sec. Thiol activated, reduced by GILT, optimally active at pH 5.5 Cholesterol dependent pore-forming toxin.

62

Action of LLO

Forms pore, interferes with iron gradients so no maturation and fusion of endosome. PLCs actually degrade vacuole.

63

Intracellular motility: Listeria

Surface protein ActA is a robust regulator of actin dep motility.

64

ActA structure.

VCA domain (mimics N-WASP) so recruits Arp2/3.
Polyproline repeats bind VASP (elongation and directionality). VASP cooperates with Arp2/3 - elongates F actin.
Does not have GBD or PRD domains so no sequestration.
Listeria

65

Listeria: actin in motility

Actin stays stationary, bacteria moves away.

66

Listeria: intracellular spread.

InlC, LLO, PlcB

67

Listeria: intracellular spread: InlC

Relaxes cortical tension by inhibiting host Tuba-WASP interactions (which provide the link between the membrane and the supporting cytoskeleton).

68

Listeria: intracellular spread: LLO

Lysis of 2nd vacuole.

69

Listeria: intracellular spread: PlcB

Closes protrusion.

70

Listeria invades which cells.

Transcytosis across M cells then into macrophages.
Also invades epithelial cells by zipper mechanism.

71

Zipper mechanism.

Contact and adherence, phagocytic cup formation and phagocytic cup closure and retraction.

72

Cells taken up by phagocytosis

Legionella, Mycobacterium, Salmonella, Coxiella.

73

Trigger mechanism

repression of secretion, interaction and secretion, formation of macropinocytic pocket, actin depolymerisation and closing of pocket.

74

Cells taken up by phagocytosis: legionella

Legionella; a parasite of amoebae and macrophages which phagocytose, so does not drive uptake itself.

75

Cells taken up by phagocytosis: mycobacterium

Complement receptors and complement opsonisation are main routes of uptake. But specific receptor unimportant.

76

Phagocytosis: salmonella

Also taken up by trigger mechanism. Requires induction of membrane ruffling requiring WAVE.

77

Phagocytosis: coxiella

Binds αvβ3 which is normally used in phagocytosis of apoptotic cells so does not induce inflammation.

78

Listeria - regulation of virulence genes

Temperature change to 37 degrees --> conformational change in mRNA of PrfA --> can be translated --> makes PrfA --> activates small chromosomal pathogenicity island.

79

Actin polymerisation cascade - spontaneous.

G actin nucleates --> unstable actin nucleus --> elongated to F actin

80

Actin polymerisation cascade - spontaneous. G actin nucleates --> unstable actin nucleus.

Inhibited by profilin

81

Actin polymerisation cascade - spontaneous. Unstable actin nucleus --> elongated to F actin.

Increased by profilin/ATP-actin. Elongation inhibited by capping protein CapZ.

82

Actin polymerisation cascade - facilitated.

Attachment of Arp2/3 to a mother filament leads to branching. Profilin/ATP-actin used in elongation, with formin as capping protein.

83

Orientation of actin filaments in comet tails.

Barbed ends towards bacteria. Propulsive force provided by polymerisation.

84

ActA

Critical to virulence in the mouse model. Sufficient for comet formation. Activates Arp2/3.

85

Actin turnover in comet tails

Cofilin, coronin and capping proteins are important. Acceleration of this maintains actin monomer pool.

86

Actin comet tails formation overview.

Arp2/3 nucleates, VASP promotes speed and directionality, favours parallel filaments. Actinin stabilises. CapZ prevent nonproductive growth.

87

Autophagy pathway

Targets cytosolic proteins and organelles to lysosomes, a key innate immune response against intracellular bacteria.
Phagophore --> autophagosome --> lysosome.

88

Listeria and autophagy

LLO triggers by damaging vacuoles. ActA protects.

89

Rho GTPases

Master regulators of the actin cytoskeleton. Recruit/activate N-WASP and WAVE.

90

GEF

Guanine nucleotide exchange factor.

91

GAP

GTPase activating protein.

92

GDI

GTPase disassociation inhibitor.

93

WAVE

Have VCA domain for Arp2/3 activation.

94

Bacterial manipulation of Rho GTPases

Toxins tend to covalently modify, secreted effectors tend to mimic.

95

Avoiding autophagy

Actin helps evade autophagy (motility or actin shel).
Phospholipases may degrade autophagosome.

96

Yersinia cell entry

Zipper mechanism into epithelial cells from basolateral side via invasins.

97

Invasins (Yersinia) - binding

Bind B integrins (usually mediate cell adhesion). Results in Rac1 remodelling and FAK recruitment. Src involved.

98

Key Rho GTPases

RhoA - stimulates focal adhesion and stress fibres
Rac1 - induces lamellipodia and ruffling.
Cdc42 - produces filopodia.

99

Invasins (Yersinia) - structure

Autotransport, not cleaved so anchored. D1, 2, 3 homo-oligomerise, D4, 5 bind integrins. Functionally mimics fibronectin (convergent evolution).

100

Yersinia resisting macrophage uptake

Uses YOPs.

101

Yersinia location

Inside epithelial cells, or in extracellular abscesses in Peyer's patches.

102

Inv locus Yersinia

Sufficient to convert E. Coli into bacteria which can penetrate cells. Codes for invasins
, critical for focal adhesion.

103

Yersinia: importance of clustering in integrin binding.

Without clustering of integrins, no signalling occurs.

104

Salmonella typhimuriusm functions of effectors in uptake

Interact with actin
Activate Rho GTPases by acting as GEFs
Activate Rho GTPases via inositol phosphate activity.

105

Salmonella typhimurium functions of effectors in uptake: interaction with actin

SipC nucleates and bundles
SipA is a molecular staple preventing ADF mediated dissassembly.
SipA potentiates SipC.

106

Salmonella typhimurium functions of effectors in uptake: activate Rho GTPases by acting as GEFs.

SopE activates Rac1, but SptP deactivates to restore actin cytoskeleton after invasion.

107

Salmonella typhimurium functions of effectors in uptake: activating Rho GTPases via inositol phosphate activity.

SopB makes PIP3 --> membrane ruffling. Binds ARNO for Arf1 activation. Arf1 + Rac1 recruit WAVE and Arp2/3.

108

Survival in vacuole: Salmonella induced filaments

Lysosomal membrane tubules induced by salmonella.

109

Survival in vacuole: Salmonella induced filaments formation

SifA --> SKIP (a linker protein to kinesin) --> would go to peripheral distribution of lysosomes in cells. PipB2 also involved.

110

Survival in vacuole: movement of SCVs to juxtanuclear region.

Near Golgi stacks.
Rab7 --> RILP --> dynactin --> dynein --> moves towards nucleus.
SseF and SSeG also involved.

111

Types of filament induced by salmonella

SNX tubules (sorting nexin), SCAMP3 tubules and LAMP negative tubules.

112

Salmonella - inducing cell death.

SlrP interacts with redox protein thioredoxin to cause apoptosis. SipB activates caspase 1 to cause macrophage death.

113

Salmonella: inhibition of immune response

NFkB pathway and mRNA

114

Salmonella: inhibition of immune response: NFkB pathway

Ubiquitin ligases IpaH and SspH1 are E3 ubiquitin ligases. Affects NFkB pathway and hence IL-8 production.

115

Salmonella: inhibition of immune response: mRNA

SpvC irreversibly removes phosphates reducing cytokine mRNA

116

Role of SPI-1 in salmonella uptake and cell infection.

Transcytosis across M cells.
Macrophage apoptosis and release of bacteria.
Uptake into cells.

117

Role of SPI-2 in salmonella uptake and cell infection.

Growth inside macrophages.

118

Salmonella divergence from E coli.

Acquisition of factors for intestinal colonisation - SPI-1
Acquisition of ability to cause systemic disease - SPI-2
Acquisition of ability to infect warm-blooded hosts.

119

Salmonella regulation of virulence genes.

Mg++/Ca++ high in gut lumen.
PhoPQ inactive in high salt conditions --> transcriptional activators like HilA --> SPI1 active.
PhoPQ active --> SPI-1 repressed, SPI-2 activated.

120

Salmonella effector translocation system

T3SS

121

SopB and SopE interactions in Salmonella

SopB generates PIP3, eventually recruits Arf1. SopE activates Rac1. Together they recruit WAVE.

122

Understanding salmonella infection

In mouse: bacteria invade, escape and infect many more cells.
In cultured macrophages: invade and replicate intracellularly.
In humans: rarely escapes gut.

123

Salmonella intracellular survival.

SPI-1 effectors --> early SCV formation.
Rabs are key to SCV formation and maturation.
Luminal environment triggers SPI-2 expression.
SPI-2 effectors maintain the vacuole, induce filaments and possibly have a role in egress.

124

Positioning of SCV.

SseF and SseG maintain. Tether in a Golgi associated manner. Promote interactions with dynein.

125

Salmonella typhi and paratyphi

Causes typhoid fever, a systemic disease.

126

Non typhoidal salmonella

Salmonella enterica serovars typhimurium (mouse is natural host in which it causes typhoid).

127

Number of SPIs

21, but 1 and 2 are the most studied

128

SPI-1 effectors --> early SCV formation.

Consider for entry
SopB recruits Rab5.

129

Salmonella: avoiding delivery of acid hydrolases

Normally: cation-independent mannose-6-phosphate receptor delivers lysosomal hydrolases from TGN to early endosomes.
SNX1 retrieves these vesicles back to the TGN.
SNX1 binds PI3P produced by SopB, so is localised to near the SCV to protect it.

130

Sensing the luminal environment to express SPI-2 effectors.

SsrAB senses acidic environment and limitation of Pi. SsrB is the RR.
Causes transcription of T3SS and effectors.

131

SCV maturation to intermediate SCV

Rab5 replaced by Rab7 (migration to perinuclear region).
SCV fuses with endosomes containing LAMP1 and vATPase.

132

SPI-2 encodes

A type III secretion system.
A two component system.
Effector proteins.

133

Interfering with NADPH oxidase - A. phagocytophilum

A. phagocytophilum interferes with assembly of NADPH oxidase subunits in inclusion membrane. and blocks activation of NADPH with phorbol myristic acetate.

134

Interfering with NADPH oxidase - Listeria

Listeria ribosylate Rab5 to inactive to prevent NADPH oxidase mediated killing before escaping vacuole.

135

Interfering with NADPH oxidase - Salmonella

Avoid recruitment.

136

SifA

Required for vacuole integrity. Anchored to SCV membrane.
SifA --> recruits SKIP --> reroutes M6PR, hydrolases secreted into extracellular medium instead. Rab9 retrieves M6PR from the PM.

137

Salmonella induced filament formation

PipB2 recruits kinesin.
SifA recruits SKIP, which activates kinesin.
Kinesin moves away from nucleus.
Generates Sifs, since SCV anchored by SseF/SseG.

138

SCV movement to perinuclear region.

Rab7 binding RILP and then dynein/dynactin motor complex, salmonella containing vacuole moves towards nucleus.

139

S. typhimurium broad host specificity

GtgE cleaves Rab32 which is necessary for lysosomal mediated death of S. typhi.

140

Cytolethal typhoid toxin exocytosis

Salmonella.
Dependent on Rab27l

141

Salmonella T3SS

Similar to flagella.

142

Bacteria taken up by trigger mechanism

Salmonella, Shigella.

143

Shigella invasion site

Transcytoses M cells.
Taken up by macrophages, induce apoptosis.
Invades epithelial cells from the basolateral side.

144

Shigella general

Causes bacillary dysentry.
Shigella dysenteriae, Shigella flexneri, Shigella sonnei, Shigella boydii.

145

Shigella regulation of invasive phenotype

The virulence plasmid is activated by VirF, a transcriptional regulator activated by physiological temperature. This causes transcription of VirF and VirB, which are also regulated by EnvZ-OmpR, CpxA-CpxR

146

Shigella effectors

IpgD (like SopB), IpaA (binds vinculin), IpgB1 activates Rac1.
IpaC is part of translocon, but indirectly activates Rac1 and Cdc42.

147

Escaping the vacuole: Shigella

Unknown mechanism. IpgD recruits Rab11. Unknown mechanism involves IpaB and IpaH. Possibly destabilising vacuole membrane.

148

motility: Shigella

IcsA for actin, VirA to sever microtubules.

149

IcsA structure and function.

Shigella. Identified in transposon mutagenesis.
Autotransported by Ctd domain. Ntd has glycine rich repeats. Binds N-WASP, activates Arp2/3.

150

VirA: function.

Microtubule network hinders shigella motility. VirA is key to severance, controversy as to how - Yoshida suggested cysteine protease activity.

151

Actin motility with branched actin

Listeria and Shigella.
Need ADF/cofilin, capZ and profilin.

152

Shigella: inducing cell death

IpaB activates caspase 1 causing macrophage death.

153

Shigella: inhibition of immune response: avoiding autophagy.

Actin based motility, actin shield and IcsB shield (competitively inhibits binding of autophagy related genes).

154

Shigella: intracellular spread.

Poorly characterised. Cell-cell junctions are subverted.

155

Mechanism of actin tails in Shigella

IcsA binds N-WASP. This binds Arp2/3 initially, and then feeds actin monomers onto the barbed end, propelling the bacterium away.

156

Role of actinin

cross-links actin.

157

Rickettsia motility

Doesn't use Arp2/3. Sca2 mimics formin to to generate unbranched acting polymers.

158

Determinants of vesicular transport

Membrane lipid composition
Membrane associated regulatory proteins
Lumenal environment.

159

Cellular compartment definition

Lipid phosphoinositides
Rabs.

160

Ways to deal with lysosomal pathway

1) Uncouple early from pathway (Chlamydia, Legionella)
2) Escape vacuole (Listeria, Shigella)
3) Prevent progression to lysosome (mycobacterium)
4) Survive progression to lysosome (Coxiella)

161

LCV morphology

rER like. SldC promotes LCV-ER fusion.
Host proteins Sar1, ARF1 and Rab1 to recruit ER derived vesicles.
Recruit mitochondria.

162

Legionella secretion system

T4SS, dot-icm.

163

Number of legionella effector proteins

More than 300. Many interact with RhoGTPases or otherwise alter LCV morphology. Others provide nutrients. Examples: RalF, SldC, AnkB.

164

T4SS

Core complex spans both inner and outer membrane.
Self-assembling.
Has cytoplasmic inner membrane subcomplex with 3 ATPases. Membrane anchors link to the core complex.

165

Which bacteria use T4SSs?

H. Pylori, Brucella suis, Legionella pneumophila.

166

RalF

Sequence homology to Arf1 GEF. Arf is important in Golgi-ER retrograde transport and formation of secretory vesicles. Legionella.

167

AnkB

Recruits proteosome so that high levels of amino acids are generated by the LCV to provide nutrients. Legionella.

168

Legionella uptake

Phagocytosis.

169

Rab 1 control by Legionella.

SidM releases Rab1 from RabGDI. Recruited to LCVs. SidM converts to GTP bound form. Locks in constitutively active form by ampylation.
SidD deampylates later in infection, enabling deactivation by LepB.

170

Mycobacterial phagosome maturation block.

LAM: ManLAM blocks Ca++ rise, preventing PI3P synthesis.
PI3P is dephosphorylated due to SapM.
Trehalose dimycolate.
Rab7 is converted to its inactive GDP bound form.

171

EEA1

Tethering molecule essetial for fusion of early and late endosomes.

172

Mycobacterium: inhibition of immune response

Binding of TLR2 leads to potent pro-inflammatory cascade, and inhibits IFNy induction and induction of antigen presenting genes.

173

Mycobacterial cell wall

Lower segment
Upper segment includes LAM and PIM

174

PIM stands for

Phosphatidylinositol mannosides.

175

Granuloma progression

Shed Mtb cell wall components. Exocytosed. Induce macrophage differentiation to foam cells. Undergo necrosis.

176

Mycobacterium secretion system

five ESX systems (T7SS)

177

Mycobacterial phagosome

Highly dynamic. Contains some lysosomal markers. Accessible to early and recycling endosomes.
Indicators of trafficking arrest: retention of Rab5 . No EEA1, vATPase, Cathepsin D or Rab7.

178

Mycobacterial damage to phagosomal membrane.

ESAT-6 and CFP-10 contribute to damage. Depend on each other for stability, secreted by ESX system.

179

Mycobacterial acquisition of iron.

Early endosomes accessible due to Rab5 marker: acquires iron from these.

180

Bacterial developmental transition on cell entry: Coxiella.

Small cell variant to large cell variant. Acidification = trigger.

181

Coxiella burnetti avoidance of killing.

Uses T4SS like legionella, but not involved in avoiding lysosome as only expressed 8 hours post-infections.
Delays hydrolases.

182

Roles of Coxiella effector proteins.

Promotion of CCV integrity.
Transcriptional modification.
Preventing apoptosis and cyt c release.
Proteasome mediated degradation for nutrients.

183

Coxiella vacuolar expansion.

Induces autophagy --> giant vacuole via Cig2.
Requires recruitment of Rho GTPase and Rab1b – maintenance and acquisition of additional membranes. Expand from small to large coxiella containing vesicles.

184

Intracellular bacteria rapidly escaping cell cytoplasm.2

Shigella, Listeria

185

Intracellular bacteria remaining withing the membrane bound vesicle.

Salmonella, Legionella pneumophila, Brucella abortus or Chlamydia spp

186

Intracellular survival

Bacterial developmental transition.
Stay in the vacuole?
Manipulating the host cell

187

Manipulating the host cell

Bacteria containing compartment interacting with other compartments.
Altering host cell death
Inhibiting immune response.

188

Exiting the host cell

Host cell death.
Exocytosis.
Intracellular spread.

189

Inhibiting the immune response - mechanisms

Alter TLR binding
Alter NFkB
Alter cytokine mRNAs
Avoid autophagy.

190

Bacteria using the zipper mechanism.

Listeria, Yersinia.

191

Microorganisms and regulation of virulence

Listeria, PrfA.
Salmonella PhoPQ
Shigella VirF.

192

Host cytoskeleton

Intracellular matrix that supports both shape and function.
Actin polymerisation
Rho GTPases
PIPs.

193

Shigella disease

causes shigellosis in humans (and apes) = dysentery with imbalance of host regulation of inflammation due to bacterial —> one of the leading bacterial causes of diarrhoea worldwide with at least 100,000 deaths (mostly children in developing world
four serogroups: s. dysenteriae causes epidemics whereas s. flexneri and s. sonnei are endemic
faeco-oral transmission
invades colonic mucosa to cause destructive recto-colitis, fever, cramps and bloody stool

194

Listeria disease.

food borne
causes gastroenteritis
invasive infection = listeriosis —> infection of the CNS — meningitis and brain accesses etc (only happens in immunocompromised, neonates, elderly, pregnant women and healthy persons who have ingested very large inoculum)

195

Shigella virulence plasmid

has 220kb virulance plasmid that has mxi-spa locus that encodes T3SS and effector proteins Ipa-Ipg
VirF responds to pH, 37 degrees C, osmolarity and iron to induce VirB expression with in turn induces T3SS and effectors
also regulated by TCSs: osmotic stress (via EnvZ/OmpR) and pH (via CpxAR)

196

Shigella: IpaB and C

bind cholesterol with high affinity and insert into membranes as translocon —> disrupt membrane to allow effector entry

197

Shigella: IpgD

interacts with PIP2 to induces actin rearrangements

198

Shigella: VirA

induces Rac1/Cdc42 dependent actin polymerisation and membrane ruffles

199

Shigella: IpgB1 and B2

act as GEFs for RhoA and Rac respectively to promote remodelling

200

Shigella: IpaA

mediates localised depolymerisation of actin via vinculin —> required to close the phagocytic cup

201

SopB and SopE interactions in Salmonella

SopB generates PIP3, eventually recruits Arf1. SopE activates Rac1. Together they recruit WAVE.