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Infection and immunity > 14. Shigella and listeria > Flashcards

14. Shigella and listeria Flashcards

1
Q

what type of pathogens are shigella and listeria?

A

Facultative intracellular bacteria

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2
Q

why are shigella and listeria important?

A

regular outbreaks
serious damage caused every year

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3
Q

how do shigella and listeria infect humans?

A

Contaminated food and water so GI tract entry
entry through M cells and Goblet cells
engulf by macrophages

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4
Q

Shigella info

A

Gram negative bacillus
discovered in Japan
cause of dysentery

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5
Q

shigella flexneri

A

most frequently isolated species
60% of cases in developing world

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6
Q

shigella sonnei

A

77% cases in developed world

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7
Q

S. dysenteriae

A

cause of the Dysentery
can be lethal

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8
Q

Shigellosis

A

strong immune system clear it in 5-7 days
80-165 million cases a year
fecal-oral transmission
low ID50
very large virulence plasmid
no vaccine and emerging resistance to treatment

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9
Q

what does low ID50 mean?

A

very few bacteria is needed to infect 50% of a population (5-100)

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10
Q

Listeria info

A

gram positive bacillus or rod
motile via flagella but not at body temp
2 pathogenic listeria species

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11
Q

what is the pathogenic strain of listeria?

A

L. monocytogenes

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12
Q

listerosis

A

affects pregnant women, newborns and immunocompromised
higher ID50 - 1000 bacteria to cause infection
30% mortality
no vaccine and treat with antibiotics
prevention - good hygiene and food habits

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13
Q

why is listeria such a problem in the food industry?

A

normal pasteurisation doesn’t kill it

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14
Q

Where can listeria spread?

A

it spreads from the intestines to
lymph nodes
liver
spleen
brain
cross placenta

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15
Q

lifecycle of cytoplasmic bacteria

A
  1. entry
  2. escape from vacuole
  3. replication within the cytoplasm
  4. Manipulation of innate immunity in the cytoplasm
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16
Q

how does listeria enter the cell?

A

zipper method

17
Q

what is the zipper method of cell entry ?

A

adhesions on bacteria recognise host cell receptors
induces actin function in the host cell to engulf the bacteria

18
Q

how does shigella enter the cell?

A

the trigger method

19
Q

what is the trigger method of entry?

A

type 3 secretion system used to transfer molecules from bacteria to host
these make membrane ruffles appear to engulf the bacteria

20
Q

how is shigella gene regulation done?

A

at the DNA level using pathogenicity islands
tight controlled

21
Q

what is VirF transcription factor function in shigella regulation?

A

VirF binds VirB promoter at 37oC
VirB induces up-regulation of other virulence factors

22
Q

how is listeria gene regulation done?

A

at RNA level using PrfA

23
Q

what is PrfA function in listeria?

A

transcription factor for operon of actA, inlA, inlB
inlA and inlB are the ligand for entering the host cell

24
Q

how is PrfA regulated?

A

it is always transcribed but the Shine Dalgarno sequence is hidden from the ribosome
when it hits body temp the block melts and the Shine Dalgarno sequence is exposed

25
Q

when do shigella and listeria escape the phagosome?

A

before lysosome fusion so they either slowdown fusion or escape quickly

26
Q

how does listeria escape the phagosome?

A

use enzymes listeriolysin O (LLO) and type C phospholipase (PLC) which are active at phagosome pH
LLO bind cholesterol and make pores
disrupts the membrane and phagosome collapse
PLC used to pass through 2 membrane to infect other cells

27
Q

how does ActA help immune escape?

A

it recruits host cell proteins to hide from immune system
recruits actin to make comet tails and move around the cell

28
Q

what does ubiquitination do in infection?

A

helps hide from the immune system

29
Q

how does shigella escape the phagosome?

A

a type 3 secretion system and effector proteins IpaB

30
Q

where is the type 3 secretion system and IpaB encoded?

A

on a virulence plasmid

31
Q

why is the translocon the important part of the t3SS?

A

IpaB and IpaC form a pore
translocon binds cholesterol on the host membrane and inserts into the membrane
takes molecules from bacteria to host cells

32
Q

how does shigella get into the basal layer?

A

travels through the M cells and released under the epithelium

33
Q

what is IcsA and IcsB important for ?

A

escape from an autophagosome by shigella

34
Q

why is replication in the cells dependant on the vacuole?

A

priming site for replication
change the environment of the cytoplasm to make it better for replication using transcription factors

Infection and immunity (22 decks)

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