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Foodborne Pathogens > P0werp0int 8: Listeria m0n0cyt0genes > Flashcards

P0werp0int 8: Listeria m0n0cyt0genes Flashcards

1
Q

What is included in the PrfA regul0n?

A

virulence fact0rs

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2
Q

Fr0m what can the virulence fact0rs be transcribed?

A

-pr0m0ters 1-4

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3
Q

What are the PrfA pr0m0ters also known as?

A

PrfA b0xes

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4
Q

What is the r0le 0f PrfA b0xes / pr0m0ters?

A

binding sites f0r PrfA transcripti0nal activat0r pr0teins

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5
Q

What is the primary regulat0r 0f virulence gene expressi0n?

A

PrfA protein

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6
Q

Prior to infection, from where is the PrfA regulator protein (a.k.a activator protein) transcribed?

A

from a σA promoter

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7
Q

Explain the heat sensitive mechanism of PrfA activator protein

A

(1) σA promoter creates PrfA transcripts (of activator protein)
(2) these are not immediately translated because they contain a loop sensitive to temperature. Thus lots of PrfA builds up.
(3) Above 30 degrees, the loops melts, and there is a lot of protein translation that takes place hence the activator protein is produced.

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8
Q

Explain the positive feedback loop of PrfA production during infection

A

Additionally to the heat sensitive loop, once the activator protein is produced it can bind to its own promoter / PrfA box to induce the expression of more PrfA

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9
Q

Explain the allosteric shift in PrfA production

A

PrfA also appears to undergo an allosteric shift from a weakly active to a highly active state upon interaction with an unknown cofactor.

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10
Q

Is there a lot of horizontal gene transfer?

A

No the genome is highly conserved.

-few mutations

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11
Q

summary slide

A

Lm is a very serious food-borne infection which can result in systemic infection, meningitis or encephalitis and abortion in pregnant females.
The ability of Lm to cause disease in other organs is a result of both of intracellular spread, and the ability to cross 3 important barriers:
The intestinal barrier
The blood brain barrier
The placental barrier
It does this through the use of several well conserved virulence factors
Lm has the ability to form biofilms in factories and persist in food processing environments for years
Lm has the ability to grow in high-salt concentrations at refrigeration temperatures
Lm is of major concern to the food industry, particularly in raw milk cheeses and cold-meats

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12
Q

What is the virulence factors it produces and the mechanism of invasion?

A

(1) InLA and InLB : attachment to host intestinal cell, and engulfed in a vacuole
(2) LLO and PI-PLC : dissolves the vacuole with Listeria hence cells divide freely in the cytoplasm free of the immune system
(3) Act A: expressed at n0n-dividing side 0f listeria cells, (pr0vides directi0nal m0vement), polymerizes host cello actin and allows it to enter other cells , where they are once again in the vacuole, and they express LLo again.

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13
Q

What was the reason of the outbreak ?

A

Hot dog plant ; had to be shut down ; can persist for years in a processing plant due to biofilms!

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14
Q

How many species of Listeria are there? How many cause infection in humans?

A

Six, only L.monocytogenes causes infection

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15
Q

Is it gram + or - ?

A

Gram +

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16
Q

What is the shape?

A

Small rod

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17
Q

What are general characteristics?

A
  • non sporulating
  • motile (flagella) only between 20 and 30 degrees
  • psychrotrophic
  • facultative anaerobe
  • saphrotype
18
Q

How many serovars exist?

A

13 serovars

19
Q

Which serovars are attributed to illness?

A

95% of outbreaks are caused by 1/2a, 1/2b, or 4b

20
Q

What are the 2 ways serovars are identified?

A

Genetic Finger Printing (PFGE) or serotyping
- now whole genome sequencing is popular

For identifying strains in outbreaks we commonly use PFGE Pulsed Field Gel Electrophoresis (but only good for small sized DNA fragments)

21
Q

Can it infect protozoa?

A

Yes

22
Q

Are some people asymptomatic carriers?

A

Yes, they carry it in their gall bladder or intestine!

23
Q

Can it survive pasteurization?

A

No! Except if it is in a WBC

24
Q

What pH can it grow in?

A

Not lower than 4.4

25
Q

What salt % can it grow in?

A

10% salt

26
Q

How is heat resistance related to salt content?

A

As salt content decreases, heat resistance increases

(more resistant to heat in environments low in salt)

on the other hand , decreasing the temperature makes it more resistant in high salt foods

27
Q

What are hospitable foods for Listeria?

A
  • ham, hot dog, bologna
  • have high salt but lower temperature
  • raw cheeses also!
28
Q

When was there an important Canadian outbreak of listeria ?

A

2008 !

29
Q

What are the 2 main essential parts when identifying an outbreak?

A

1) subtyping (PFGE or serotyping)
2) communication
Pulse-Net : communicate info

30
Q

What does Pulse Net do?

A

PulseNet compares the DNA fingerprints of bacteria from patients to find clusters of disease that might represent unrecognized outbreaks.

This allows investigators to find the source, alert the public sooner, and identify gaps in our food safety systems that would not otherwise be recognized.

PulseNet uses DNA fingerprinting of bacteria making people sick, to detect thousands of local and multistate outbreaks

31
Q

What are the 2 known problems of PFGE? (pulsed field gel electrophoresis)

A

over discrimination: when you identify 2 strains as being different because their pattern is different. They are in fact the same strain.
-caused by loss of mobile genetic element

under discrimination: when you identify 2 strains as being the same because their pattern is the same; when in reality they are 2 different strains.
-caused by a shortage of patterns

32
Q

For what population is Listeria a problem?

A

Not healthy adults

-immunocompromised, the young, the old

33
Q

What is the mortality rate associated to Listeria

A

20-25%

34
Q

What symptoms can it cause?

A

septicemia, meningitis, encephalitis, endocarditis, liver abscess

35
Q

What is so weird about the incubation time?

A

Can be up to 5 weeks !

36
Q

what 3 barriers can it cross?

A

The intestinal barrier
The blood brain barrier
The Placental Barrier

37
Q

What cells does it target?

A

Mesenteric lymph node cells , via macrophages

38
Q

What usually happens when Listeria becomes systemic in the healthy adult?

A

when they have access to systemic circulation, the immune system clears the infection in healthy adults

39
Q

What happens in non healthy adults?

A
  • the immune cells carry Lm back to the liver and the spleen where they establish reservoirs of infection
  • circulate in the system targeting specific organs
40
Q

What is the fatility rate if insepticemia occurs?

A

45% chance of death

-high death in newborns also

41
Q

Can Listeria grow in high salt concentrations in refrigeration temperatures?

A

Yes.

The lower the temperature, the better it can live in high salt concentrations

Foodborne Pathogens (11 decks)

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