L13 - Shigella and Listeria

Question 1

name the type of bacteria that shigella and listeria are

Answer 1

facultivea intracellular

= can live and replicate inside and outside of host cell

Question 2

simple pathogensis of shigella and listeria

Answer 2

ingested in contaminated food

pass through M-cells in Small intestine

engulfed by macrophages on other side but escape vesicle and proliferate in cytoplasm

= can also tirck normal cells to take them in = alternatrive route to M-cells

Question 3

who discovered shigella

Answer 3

Kiyoshi Shiga

caused diarrhoea when he fed isolated bacteria to dogs

Question 4

gram stain of shigella

Answer 4

negative

Question 5

symptoms of shigellosis

Answer 5

Bloody diarrhea

fever and stomach cramps

Question 6

worldwide deaths from shigella/shigelliosis annually

Answer 6

600,000

Question 7

most commonly infected by shigella and how

Answer 7

infants and childeren in 3rd world countries

infected water - feral-oral

Question 8

what is the ID50 of shigella

Answer 8

5 bacteria
= very low

ID50 = number of bacteria required to cause disease/infection

Question 9

history of Listeria

Answer 9

origanlly named ‘bacterium’

later chnaged to ‘listeria’ in 1940

Question 10

describe shape and gram of listeria

Answer 10

gram positive rods

contains flagella at lower temperatures

Question 11

how is listeriosis/listeria transmitted and who to mainly

Answer 11

conbtaminated food

= milk products - cheese

people with wekaned immune system (pregnant,neborns)

Question 12

temperature prefferences of listeria

Answer 12

can still grow at low temps

and displays high heat reistance

= most virulence factors upregulated at 37˚

Question 13

what is the ID50 of listeria

Answer 13

10^3

much higher than shigella

Question 14

what part of the body does listeria infect

Answer 14

has access to bloodstream and lymph circulation after crossing intestinal barrier= wide range of targets

= can cross placental barrier and infect foetus
= can cross blood-brain barrier

Question 15

what are the 4 stages that all intracellular bacteria undergo

Answer 15

1. entry/invasion
2. exapse from vacuole
3. replication in cytoplasm
4. mannipulation of innate responses triggered in cytoplasm

Question 16

describe Listerias ‘Zipper’ mechanism to invade host cells

Answer 16

tricks non-phagocytotic cells to ‘engulf’ listeria

1. adhesins bidn to receptors
2. membrane engulment vai membrane protrusion

= pseuodpodia

Question 17

describe the ‘Trigger’ mechansim used by Shigella to invade host cells

Answer 17

T3SS used in same way as salmonella

1. T3SS injects effector proteins
2. cause membrane shiffling by affecting Rac1 GTPase

= produces filopodia/protrusions that disrupt membrane

3.Shigella enters

Question 18

at what temperature are shigella and listerias virulence factors unregulated

Answer 18

37˚

= but different mechanisms for detction and upregulatation

Question 19

describe the mechanims shigella undergoes to upregulate virulence factors when temp is above 37˚

Answer 19

1. high temp activates DNA gyrase to modulate supercoiling/open DNA
2. VirF is produced
3. VirF activates VirB = T3SS operon

= codes for structurala nd effector proteins

Question 20

describe listerias mechanisms to upregulate virulence factors above 37˚

Answer 20

RNA thermosenser
= prfA is a transcription factor for virlulence genes

1. at low temps PrfA mRNA forms a secondary strcuture blocking ribosome binding site
2. at high temps prfA undergoes comformational change

= can bind and be translated

3. virulence factors are transcibed

Question 21

why must listeria and shigella repaidly escape endosome/vaccuole

Answer 21

before lysosome fuses and kills bacteria within endosome

Question 22

name the 2 enzymes involved in the excape from vaccuole/endosome in listeria

Answer 22

Listeriolysin O (LLO)

Type C phospholipase (PLC)

Question 23

describe emchansim of escape from endosme by listeria (LLO + PLC)

Answer 23

1. acidic conditions of vacuole activate Listeriolysin-O (LLO)
2. binds ot cholesterol and forms pore

= membrane disruption

3. PLC helps disruption of vacuole + is important in double-membrane disruption

= cell-cell spread

Question 24

role of actA in listerias lifecycle inside cytoplasm

Answer 24

after listeria has escaped from vacuole and free inc cytoplasm

1. actA binds and wraps around bacteria
2. recruits proteins produced by host cell

= disguises bacteria by hiding within host proteins

3. produces actin commet tail to move around cell or to new host cell

Question 25

what happens if there are mutations in actA - listeria

Answer 25

no coating of host proteins to listeria = no ‘disguise’

recognised and ubiquitinated

= destroyed by host cell

Question 26

mechansism of vacuole escape - shigella

Answer 26

1. IpaB and IpaC are injceted into cytoplasm

= form pore complex

2. disrupt phagosomal membrane = escape

Question 27

what is IscA from shigella similarv to in function in listeria

Answer 27

actA

= both form polymerisation of `actin to form ‘actin-commet’

Question 28

role of IscB in shigella (think of IscA)

Answer 28

iscB is recruited to IscA and hides it

= cannot be targetted by autophagy pathway

= no IscB = autolysosome forms and destroys bacteria

Question 29

summarise shiggella vs listerias diuffernt poroteins and pathways for:
1.entry
2.lysis of vaccuole/escape
3. cell-cell spread

Answer 29

1. Entry:
   listeria - adhesins - ‘zipper’ mechansim’
   shigella - T3SS
2. Lysis:
   listeria - LLO + low pH
   shigella - T3SS - IpaB + IpaC

movement:
listeria - ActA
shigella - IscA