14. Shigella and listeria Flashcards
what type of pathogens are shigella and listeria?
Facultative intracellular bacteria
why are shigella and listeria important?
regular outbreaks
serious damage caused every year
how do shigella and listeria infect humans?
Contaminated food and water so GI tract entry
entry through M cells and Goblet cells
engulf by macrophages
Shigella info
Gram negative bacillus
discovered in Japan
cause of dysentery
shigella flexneri
most frequently isolated species
60% of cases in developing world
shigella sonnei
77% cases in developed world
S. dysenteriae
cause of the Dysentery
can be lethal
Shigellosis
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
what does low ID50 mean?
very few bacteria is needed to infect 50% of a population (5-100)
Listeria info
gram positive bacillus or rod
motile via flagella but not at body temp
2 pathogenic listeria species
what is the pathogenic strain of listeria?
L. monocytogenes
listerosis
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
why is listeria such a problem in the food industry?
normal pasteurisation doesn’t kill it
Where can listeria spread?
it spreads from the intestines to
lymph nodes
liver
spleen
brain
cross placenta
lifecycle of cytoplasmic bacteria
- entry
- escape from vacuole
- replication within the cytoplasm
- Manipulation of innate immunity in the cytoplasm
how does listeria enter the cell?
zipper method
what is the zipper method of cell entry ?
adhesions on bacteria recognise host cell receptors
induces actin function in the host cell to engulf the bacteria
how does shigella enter the cell?
the trigger method
what is the trigger method of entry?
type 3 secretion system used to transfer molecules from bacteria to host
these make membrane ruffles appear to engulf the bacteria
how is shigella gene regulation done?
at the DNA level using pathogenicity islands
tight controlled
what is VirF transcription factor function in shigella regulation?
VirF binds VirB promoter at 37oC
VirB induces up-regulation of other virulence factors
how is listeria gene regulation done?
at RNA level using PrfA
what is PrfA function in listeria?
transcription factor for operon of actA, inlA, inlB
inlA and inlB are the ligand for entering the host cell
how is PrfA regulated?
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
when do shigella and listeria escape the phagosome?
before lysosome fusion so they either slowdown fusion or escape quickly
how does listeria escape the phagosome?
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
how does ActA help immune escape?
it recruits host cell proteins to hide from immune system
recruits actin to make comet tails and move around the cell
what does ubiquitination do in infection?
helps hide from the immune system
how does shigella escape the phagosome?
a type 3 secretion system and effector proteins IpaB
where is the type 3 secretion system and IpaB encoded?
on a virulence plasmid
why is the translocon the important part of the t3SS?
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
how does shigella get into the basal layer?
travels through the M cells and released under the epithelium
what is IcsA and IcsB important for ?
escape from an autophagosome by shigella
why is replication in the cells dependant on the vacuole?
priming site for replication
change the environment of the cytoplasm to make it better for replication using transcription factors
