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Human Microbial Diseases Block 1 > Type 3 Secretion Systems > Flashcards

Type 3 Secretion Systems Flashcards

1
Q

What is the main function of T3SSs?

A

Deliver bacterial proteins directly to the host cell

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2
Q

What is the advantage of having a T3SS?

A

Allows for a more targeted effect

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3
Q

Where are T3SS-encoding genes found?

A

Usually clustered as part of a large pathogenicity island on the chromosome or a plasmid

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4
Q

How are the genes for T3SS passed?

A

Horizontal gene transfer

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5
Q

Name the types of T3SSs

A
  • Ysc family
  • Inv-Mxi-Spa family
  • Ssa-Esc family
  • Hrc-Hrp1 and Hrc-Hrp2 families
  • Rhizobiales family
  • Chlamydiales family
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6
Q

What bacteria was the Ysc family first described on?

A

Yersinia species

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7
Q

How many Ysc T3SSs are found on each cell?

A

10-30 per cell

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8
Q

What bacteria have T3SSs in the Ysc family?

A
  • Alpha-proteobacteria -> Bordetelia sp.
  • Gamma-proteobacteria -> Yersinia, Pseudomonas and Vibrio sp.
  • Delta-proteobacteria -> Desulfovibrio sp.
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9
Q

Describe the structure of the Ysc T3SS

A

Short with a hollow needle (60nm)

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10
Q

What is the function of the Ysc T3SS?

A

Confer resistance to the innate immune response by triggering apoptosis in macrophages

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11
Q

What type of pathogen does a Ysc T3SS suggest?

A

An extracellular pathogen

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12
Q

What is the Inv-Mxi-Spa family named after?

A

The Inv-Spa T3SS (SP-1) of Salmonella sp and the Inv-Mxi T3SS of the Shigella sp.

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13
Q

How many SP-1 are there per cell?

A

10-100 per cell

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14
Q

How many Inv-Mxi per cell?

A

50-100 per cell

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15
Q

What is the needle length of Inv-Mxi-Spa family?

A

40 nm

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16
Q

Describe the action of the Inv-Mxi-Spa family

A

Both systems trigger bacterial uptake by non-phagocytic cells by altering actin polymerisation

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17
Q

What type of pathogen is Inv-Mxi-Spa family indicative of?

A

Invasive pathogens

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18
Q

What is the Ssa-Esc family named after?

A

Named after the archetypal Esc T3SS of E. coli and the Ssa system in Salmonella enterica

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19
Q

What does the Esc T3SS of E. coli promote?

A

Adherence to epithelial cells

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20
Q

Where is the Ssa system encoded in Salmonella enterica?

A

SPI-2

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21
Q

How many SPI-2 are there per cell?

A

1-10

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22
Q

Describe the structure of the Esc needle

A

Has a long flexible filament (around 120 nm)

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23
Q

What is the function of the Ssa-Esc family T3SSs?

A

Allows invasion/survival in a host cell and adherence to epithelial cells

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24
Q

Name some species that have Hrc-Hrp1 and Hrc-Hrp2 T3SSs

A
  • Xanthomonas sp.
  • Pseudomonas syringae
  • Ralstonia solanacearum
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25
Q

Describe the structure of the T3SSs in the Hrc-Hrp1 and Hrc-Hrp2 families

A
  • Injectisome has a long, flexible pilus

- 2 microm length and 7nm diameter

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26
Q

Why are the T3SSs in the Hrc-Hrp1 and Hrc-Hrp2 families so long?

A

Allows transversal of the thick plant cell wall

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27
Q

What bacterial species have T3SSs from the Rhizobiales family?

A

Rhizobium sp.

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28
Q

What does the Rhizobium sp. infect and cause?

A

Form symbiotic relationships with plants that result in the formation of nodules on the roots of leguminous plants

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29
Q

Describe the location of the genes coding for the translocation apparatus in the chlamydiales family of T3SS

A

Located in 3 loci

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30
Q

How many proteins make up the main structural components of T3SSs?

A

20

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31
Q

What is the channel width of T3SSs?

A

0.1-2 nm

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32
Q

What does the translocon/tip do?

A
  • Interacts with the host cell membrane directly

- Usually forms a pore in the host membrane

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33
Q

What do the tip proteins do?

A

Regulate needle length

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34
Q

What does the needle filament do?

A
  • It’s hollow

- Conduit through which proteins pass

35
Q

What does the base do?

A

Spans the outer and inner membrane

36
Q

What is the export apparatus?

A

A gated pore that controls export

37
Q

What do the cytoplasmic components do?

A

Controls/guides protein delivery

38
Q

What do chaperones do?

A

Keep the proteins in an inactive form in the bacteria until they are ready for translocation

39
Q

Describe the bipolar model of injectisome assembly

A
  • Assembly starts in 2 places
  • Outer membrane (OM) secretin ring joins to inner membrane protein (SctD)
  • Concurrently the inner ring assembles on the inner membrane
  • The OM ring and the IM complex join together
  • Integration of the 2 assemblies into 1 complex allows subsequent recruitment of the cytoplasmic components
  • This leads to a functional T3SS
  • First secretes early substrates and components of the inner rod and needle filament proteins
40
Q

What did T3SSs descend from?

A

Flagella

41
Q

How do non-flagellar T3SSs spread?

A

As virulence cassettes via horizontal gene transfer

42
Q

How are flagellar systems transferred?

A

Mostly transferred vertically

43
Q

What is the length of flagella?

A

10-20 microm

44
Q

What is the infectious dose of EPEC?

A

10^8 - 10^10 cells

45
Q

What does EPEC cause in humans?

A

Diarrhoea (bloody diarrhoea in infants)

46
Q

What is the site of damage of EPEC?

A

Ileum

47
Q

What toxin does EPEC use?

A

Proteases

48
Q

What is the treatment of EPEC?

A
  • Self-limiting with oral rehydration

- Antibiotics rarely

49
Q

What does STEC stand for?

A

Shiga toxin producing E. coli

50
Q

What does EHEC/STEC cause?

A

Bloody diarrhoea and kidney disease

51
Q

What is the infectious dose of EHEC/STEC?

A

50-500 cells

52
Q

What is the site of damage of EHEC/STEC?

A

Colon

53
Q

What does shiga toxin target?

A

Targets microvasculature and the cells around the kidney

54
Q

What is the main reservoir of EHEC/STEC?

A

Cattle

55
Q

How doe EPEC/EHEC adhere?

A
  • Attach through A/E lesions
  • Lose microvilli in the process
  • Sit atop actin-rich pedestals on the epithelial surface forming an intimate attachment to the host
56
Q

What is intimin encoded by?

A

The eaeA gene

57
Q

What was Hp90 renamed to?

A

Translocated intimin receptor (Tir)

58
Q

Can EPEC/EHEC mutants lacking Tir cause disease?

A
  • Avirulent in experimental models
  • No diarrhoea or intestinal inflammation
  • No A/E lesions detected
59
Q

What are required for EPEC/EHEC colonisation?

A
  • Tir/intimin interactions

- Functional T3SS

60
Q

Is there a vaccine for EPEC/EHEC?

A

Products have been approved for use in cattle but none are available for use in humans

61
Q

What are the predominant serovars that cause non-typhoidal salmonellosis?

A
  • S. enteritidis
  • S. typhimurium
  • S. heidelberg
  • S. newport
62
Q

What does T3SS1 on Salmonella do?

A

Delivers effectors that mediate invasion of non-phagocytic cells and initial formation of SCV

63
Q

What does T3SS2 on Salmonella do?

A

Mediates subsequent SCV biogenesis

64
Q

What does SPI1 encode?

A

Encodes T3SS1

65
Q

What processes are the effectors encoded on SPI1 involved in?

A
  • Cytoskeletal rearrangements
  • Triggering of cell entry
  • Apoptosis
  • Loss of electrolytes
  • Inflammation
66
Q

What does SPI2 encode?

A

T3SS2

67
Q

What is SipA encoded on?

A

SPI1

68
Q

What does SipA contribute to?

A
  • Contributes to epithelial cell invasion by catalysing actin polymerisation and bundling of actin filaments
  • Facilitates survival of emerging cytosolic Salmonella and/or initiation of replication in this environment
69
Q

Do cytosolic Salmonella or SCV Salmonella replicate faster?

A

Cytosolic Salmonella

70
Q

Describe the pathogenesis of Shigella

A
  • Shigella crosses the epithelium via M cells and is endocytosed by macrophages
  • Shigella escape from the macrophage, inducing their pyroptotic cell death and inflammation
  • Shigella reaches the epithelium’s basolateral surface and is taken up by macropinocytic pathways
  • Back inside the epithelial cell, the bacterium induces lysis of the phagosome in which they are contained, and begins to disseminate intracellularly
71
Q

How many T3SS types does Shigella have?

A

1 type - can produce different effects depending on the cell that it’s in

72
Q

Which T3SS components of Shigella induce pyroptotic cell death in the macrophage?

A
  • IpaB -> effector
  • Mxil -> rod
  • MxiH -> needle
  • IpaH7.8
73
Q

What type of death is pyroptosis?

A

Uncontrolled inflammatory death

74
Q

What Shigella effector proteins block epithelial cell death?

A
  • VirA
  • OspC3
  • IpgD
75
Q

Can effectorless T3SS allow Shigella to escape from epithelial cells?

A

Yes

76
Q

What are the properties of T3SS effectors?

A
  • Hallmark of T3SS is their lack of a conserved cleavable signal sequence
  • Instead the sequences of effectors seem to be enriched for serine, threonine, isoleucine and proline amino acids at the N-terminus -> limited peptide sequence conservation
  • This N-terminal sequence can be sufficient to export the protein via either the flagellar or NF-T3SSs
  • Given lack of an obvious amino acid-based signal, the secondary structure of the 5’ end of the effector’s mRNA was proposed as an alternative
77
Q

What do chaperones do?

A

Play a role in directing NF-T3SS effectors to the correct secretion machinery

78
Q

Name some examples of T3SS inhibitors

A
  • Salicylidene acyl hydrazides
  • N-hydroxybenzimidazoles
  • Anti-PcrV antibodies to P. aeruginosa
79
Q

How do salicylidene acyl hydrazides work?

A

Decreases T3SS expression in Yersinia sp.

80
Q

How do N-hydroxybenzimidazoles work?

A
  • Interact with LcrF, a transcriptional activator of T3SS in Yersinia
  • Appears active against a broad range of LcrF-like regulators so could be used more widely than to target T3SS
81
Q

What are anti-PcrV antibodies to P. aeruginosa used to treat?

A

May help treat patients with respiratory tract inflammation and cystic fibrosis

82
Q

What are the actions of T3SS inhibitors?

A
  • Block T3SS assembly
  • Block host interaction
  • Block effector secretion
83
Q

What are the advantages of using T3SS inhibitors over antibiotics?

A
  • No resistance

- Highly specific so won’t affect the rest of the microbiota

Human Microbial Diseases Block 1 (7 decks)

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