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MB3001 > L10 Listeria > Flashcards

L10 Listeria Flashcards

1
Q

Examples of invasive pathogens

A

Shigella, Listeria monocytogenes

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2
Q

What disease does Shigella cause?

A

Bacillary dysentery - inflammatory colitis resulting in bloody diarrhoea

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3
Q

Features of Listeria monocytogenes

A

Gram positive bacteria (thick peptidoglycan layer)
Rod-shaped
Motile (at 25℃, not at 37℃)
Psychrotrophic (can replicate in refrigerated food)
Food borne invasive pathogen

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4
Q

How does Listeria monocytogenes gain access to underlying immune cells?

A

It has to invade gut epithelial cells to help it spread systemically throughout the body where it can colonise the liver & spleen and cause systemic disease - often fatal

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5
Q

What disease does Listeria monocytogenes cause?

A

Listeriosis

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6
Q

Symptoms of listeriosis?

A

Symptoms range from mild flu-like illness to infections of CNS (meningitis, encephalitis) and ultimately, septicaemia

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7
Q

Can Listeria cross the placental barrier?

A

Yes

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8
Q

What is the most common bacterial killer of foodborne origin?

A

Listeria

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9
Q

What is the fatality rate associated with Listeriosis?

A

20-40%

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10
Q

Who does Listeria mainly affect?

A

YOPIs = young, old, pregnant, immunocompromised

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11
Q

What are pregnant women advised not to eat (due to Listeria risk)?

A

Unpasteurised dairy

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12
Q

What was the first outbreak to link listeriosis with food?

A

Coleslaw Outbreak in Canada (1981)

infected sheep → fertiliser → cabbage → coleslaw → humans

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13
Q

Does L. monocytogenes have a high or low infectious dose in susceptible people?

A

Low

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14
Q

How does L. monocytogenes enter the body?

A

Through the gastrointestinal tract

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15
Q

Does L. monocytogenes survive the low pH of the stomach?

A

Yes, it is also quite bile-resistant

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16
Q

Describe the pathogenesis of Listeriosis

A
  • Adherence of bacteria to epithelial cells
  • Mediated by Internalin A & B
  • Internalin A binds to E-cadherin (InlA most important in terms of getting across gut barrier) → signalling cascade within host epithelial cell
  • Must colonise gut to invade
  • InlB binds Met (more important for ubiquitous spread of bacteria to liver & spleen)
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17
Q

At what stage of listeriosis pathogenesis is Internalin A important?

A

Important early on as Listeria gains hold

InlA receptor only found in certain places i.e. intestines

18
Q

At what stage of listeriosis pathogenesis is Internalin B important?

A

Important in systemic spread of disease in later stages

InlB receptor is ubiquitous

19
Q

Human primate model of listeriosis?

A

Good uptake, good spread, poor model (unethical & expensive)

20
Q

Mouse model of listeriosis?

A

Poor uptake (InlA doesn’t bind well to mouse E-cadherin), good spread (InlB binds well to mouse Met protein), poor model overall because you have to give very high doses of Listeria to a mouse in order to establish an infection (poor oral infection)

21
Q

Guinea pig/ rabbit model of listeriosis?

A

Good uptake (adherence), poor spread, poor model (poor systemic infection)

22
Q

Gerbil model of listeriosis?

A

Good uptake, good spread, good model? (has never been tested)

23
Q

To what does Internalin A bind?

A

E-cadherin

24
Q

To what does Internalin B bind?

A

Met protein

25
Q

How have scientists tried to improve the mouse model as a model for listeriosis?

A

Transgenic mice - mice expressing human E-cadherin gene (hE-cad), expect good uptake & spread, but still a poor model. Don’t get disease & don’t know why.
Another approach: try murinise the Listeria - make Listeria more able to infect the natural mouse. Mutate InlA protein so that it interacts better with mouse E-cad. Predict good uptake & spread, good model?

26
Q

What toxin does Listeria produce?

A

Listerolysin O (LLO)

27
Q

What type of toxin is Listerolysin O (LLO)?

A

A cholesterol-dependent pore-forming toxin

28
Q

How does LLO work?

A
  • LLO produced by Listeria & bursts the phagosome
  • Bacteria is released & can replicate
  • Spread to adjoining cells with a protein called ActA
  • ActA polymerises actin to push bacteria into adjoining cells
  • Finds itself in a double membrane vacuole, which is burst by LLO & PlcA/B (lecithinase) to release bacteria
29
Q

LLO is only active at?

A

low pH - doesn’t destroy cell membrane because its inactivated by normal pH of the cytoplasm once out of the phagosome

30
Q

What is the name of the sequence in LLO?

A

PEST sequence - AA seq that targets proteins for degradation by the host proteasome, so LLO is rapidly destroyed once it’s released from phagosome

31
Q

Where is LLO relatively inactive?

A

Cytoplasm

32
Q

True or False: LLO mutants are 10⁵-fold less virulent than WT (Bacillus subtilis LLO+ can gain access to cell cytoplasm)

A

True

33
Q

Besides LLO, what does Listeria also produce?

A
  • Lecithinase (PlcA and PlcB) - cell-to-cell spread

- Metalloprotease (MpI) - processing lecithinase

34
Q

What features are at the end of the Listerolysin O toxin?

A

Acidic traits & transmembrane helices (these bits form the pore at low pH)

35
Q

What happens when Listeria induces its own uptake by receptor-mediated phagocytosis?

A

Listeria is entrapped in a phagosome, which it destabilises by expressing LLO and 2 broad-range phospholipases (PC-PLC, PI-PLC), allowing bacterial escape.

36
Q

How can LLO alter host physiology?

A
  • Ion flux (Ca2+ & K+ loss)
  • Mitochondrial fragmentation
  • Histone modification
37
Q

What gene encodes LLO?

A

HLY gene

38
Q

Do Listeria produce flagella during infection?

A

No - they are non-motile at 37℃

but they can move via rearranging actin filaments in host target cell

39
Q

What does actin rearrangement by Listeria require?

A

ActA - initiates actin polymerisation

40
Q

All genes (except InlA & InlB) are located on a single operon controlled by what regulator?

A

PrfA (which is activated by temp, pH & salt). Then InlA & InlB are made - makes sense because bacteria have to attach & invade before anything else.

41
Q

What is LntA?

A

LntA = Listeria nuclear targeted protein A

may affect gene expression of host cell

MB3001 (15 decks)

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