14. Shigella and listeria

Question 1

what type of pathogens are shigella and listeria?

Answer 1

Facultative intracellular bacteria

Question 2

why are shigella and listeria important?

Answer 2

regular outbreaks
serious damage caused every year

Question 3

how do shigella and listeria infect humans?

Answer 3

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

Question 4

Shigella info

Answer 4

Gram negative bacillus
discovered in Japan
cause of dysentery

Question 5

shigella flexneri

Answer 5

most frequently isolated species
60% of cases in developing world

Question 6

shigella sonnei

Answer 6

77% cases in developed world

Question 7

S. dysenteriae

Answer 7

cause of the Dysentery
can be lethal

Question 8

Shigellosis

Answer 8

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

Question 9

what does low ID50 mean?

Answer 9

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

Question 10

Listeria info

Answer 10

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

Question 11

what is the pathogenic strain of listeria?

Answer 11

L. monocytogenes

Question 12

listerosis

Answer 12

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

Question 13

why is listeria such a problem in the food industry?

Answer 13

normal pasteurisation doesn’t kill it

Question 14

Where can listeria spread?

Answer 14

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

Question 15

lifecycle of cytoplasmic bacteria

Answer 15

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

Question 16

how does listeria enter the cell?

Answer 16

zipper method

Question 17

what is the zipper method of cell entry ?

Answer 17

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

Question 18

how does shigella enter the cell?

Answer 18

the trigger method

Question 19

what is the trigger method of entry?

Answer 19

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

Question 20

how is shigella gene regulation done?

Answer 20

at the DNA level using pathogenicity islands
tight controlled

Question 21

what is VirF transcription factor function in shigella regulation?

Answer 21

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

Question 22

how is listeria gene regulation done?

Answer 22

at RNA level using PrfA

Question 23

what is PrfA function in listeria?

Answer 23

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

Question 24

how is PrfA regulated?

Answer 24

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

Question 25

when do shigella and listeria escape the phagosome?

Answer 25

before lysosome fusion so they either slowdown fusion or escape quickly

Question 26

how does listeria escape the phagosome?

Answer 26

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

Question 27

how does ActA help immune escape?

Answer 27

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

Question 28

what does ubiquitination do in infection?

Answer 28

helps hide from the immune system

Question 29

how does shigella escape the phagosome?

Answer 29

a type 3 secretion system and effector proteins IpaB

Question 30

where is the type 3 secretion system and IpaB encoded?

Answer 30

on a virulence plasmid

Question 31

why is the translocon the important part of the t3SS?

Answer 31

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

Question 32

how does shigella get into the basal layer?

Answer 32

travels through the M cells and released under the epithelium

Question 33

what is IcsA and IcsB important for ?

Answer 33

escape from an autophagosome by shigella

Question 34

why is replication in the cells dependant on the vacuole?

Answer 34

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