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98 Cards in this Set
- Front
- Back
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Describe listeria monocytogenes
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G+
Rod shaped |
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What kind of a pathogen is it?
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Intracellular
Foodborne Facultative |
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Is this pathogenic for most ppl?
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No, generally doesn't hurt healthy ppl
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Does this form spores?
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No
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Does it form biofilms?
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Yes
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At what T does it grow?
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4 degrees
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At what T is it motile?
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16 degrees
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What is the only known pathogenic Listeria species?
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L. monocytogenes
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Where is L. monocytogenes found (env't)?
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Soil
Water Food products (unpasteruized milk, meat, vegetables, soft cheese) |
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What host barriers can L. monocytogenes cross?
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Intestinal-epithelial (soft tissue)
Fetoplacental Blood-brain |
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Who does this bact mainly affect?
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Immunocompromised
Infants Elderly Pregnant women |
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What are clinical manifestation of this bact infection?
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Gastroenteritis
Meningitis (25% mortality rate) Miscarriages in pregnant women |
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Where is listeria mainly found in the body?
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Blood or typically sterile fluids
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What are the successive steps of Listeriosis?
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Contaminated food
Goes to intestine LN Liver Spleen Then gets into blood stream |
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What are the most common clinical isolates of L. monocytogenes?
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4b
1/2a 1/2b |
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What is the mortality rate of this bact?
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20-30%
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What first defines listeriosis?
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Bacteria in blood stream
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Who makes up greatest number of infected people (which gp of ppl)?
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Pregnant women (1/3 of the cases)
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Where do most of the Quebec listeris diseases come from?
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cheese (50% of them)
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What is the size of the L. monocytogenes genome?
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2.9 Mbp
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What is similar about the listeria genomes?
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Similar organizations
Circular genome Related to B. subtilis |
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How many genes are unique to L. monocytogenes?
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270 genes
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What are these genes mostly for?
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Intracellular growth
Survival |
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Where are most of these genes found?
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All on single gene: LIPI-1 (pathogenicity island)
(Except lnl A and B) |
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What regulates this pathogenicity island?
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Prfa TF
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What are the virulence factors of L. monocytogenes?
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prfA
plcA and B actA inlAB mpl |
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What are plcA and B?
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Phospholipases (Pi-PLC and PC-PLC)
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What is hly?
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Listeriolysin O (LLO)
Pore forming toxin |
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What is actA responsible for?
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Actin based motility
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What is mpl? What is its purpose?
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Secreted metalloprotease
Helps export and activate phospholipases |
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What is inlAB responsible for?
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Entry (gene at different location)
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What is PrfA?
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TF that regulates expression of virulence genes
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When is PrfA expressed?
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at 37 degrees
(done through a thermosensor) |
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Why isn't PrfA expressed at lower T?
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At low temp, the structure at the 5' UTR prevents interaction with ribosome and thus expression
->Prevents ribosome from binding the Shine Dalgarno sequence (.: PrfA can't be translated) |
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Why is 37 degrees significant?
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Human body temp
Lysteria can express this TF in our bodies |
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How does L monocytogenes enter cells?
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Induces its own uptake into phagocytic cells
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What is the zipper for listeria? (mode of bacterial entry)
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Involves InlA and B
Bacterial surface ptn binds surface receptor Very localized Induces downstream signalling |
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Which other bacteria uses this method?
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Yersinia
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What is the other mode of bacterial entry?
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Trigger mechanism
(Used by Shigella and Salmonella) |
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Describe the trigger mechanism
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Type 3 SS
Inject bacterial ptns Regulate actin and cytoskeleton changes => More GLOBAL changes throughout the cell |
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Compare ad contrast Zipper vs trigger mechanisms
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Zipper:
Surface ptn bound to host receptor Very localized: local actin accumulation, localized engulfment Trigger: -T3SS -Bacteria inject toxins that manipulate host cytoskeleton -"Global" changes to the cytoskeleton |
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Overview of Listeria intracellular lifecycle
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Induces its own uptake into non-phagocytic cells
Binds through surface receptros Enclosed in phagosome Lysotoxin O: lyses vacuole Bacterial replication =>ActA: hijacks host cytoskeleton ->Forms tails where it binds and infects other cells |
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What are the internalins important for?
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Entry (Inl A and B for L .monocytogenes)
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How many members are part of the lysteria internalin family?
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25
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What is the length of the LRRs in the internalins?
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Variable (3-28)
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What are the 3 categories of Inl?
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1) LPXTG: covalently linked to p/g
2) GW: not covalently linked to p/g, but still bound to cell wall through electrostatic charges (GW can be bound or secreted) 3) Secreted: Secreted from bacteria |
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Describe the internalin structure?
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Has repeats
Each repeat has a B-strand Ptn-ptn interactions |
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Describe InlA (how many aa, LRRs)
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800 aa
15 LRRs structure: signal peptide--15 LRRs--- IR--LPXTG |
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What is the LRR region for?
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Found in mammalian ptns
Mainly involved in ptn-ptn interactions |
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What is the IR?
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Inter-repeat region
->Ig like fold |
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What does LPXTG do?
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Covalently links to p/g
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Where does InlA bind?
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Binds E-cadherin
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What ptn is responsible for species specificity (mice vs humans)?
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Proline 16
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Where does InlA mediate entry?
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PRomotes bacterial entry into the intestinal epithelium
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Describe InlA mediated entry.
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Binds cell adhesion receptor E-cadherin
Cytoplasmic tail of E-cadherin interacts with B-catenin B-catenin binds to the actin binding ptn a-catenin This complex provides E-cadherin with the necessary link to the actin cytoskeleton to drive entry |
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What might lnlA be responsible for during pregnancy?
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Transversal of fetoplacental barrier
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Describe lnlB
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67 kDa ptn
7.5 LRRs Inter repeat region (IR) B-repeat is unstructured |
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How is lnlB found in the system
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Soluble form
Non covalently bound to the bacterial cell wall |
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What does lnlB bind?
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Lipoteichoic acid (LTA)
Heparin |
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How many GW domains bind LTA?
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3
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What is Inl B responsible for?
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Entry into many different cell types
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What does Inl B bind?
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Met Reeptor tyrosine kinase (hepatocyte growth factor (HGF) receptor)
Also binds gC1q receptor |
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Does InlB compete with HGF for the met receptor?
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No, becuase t binds a different area of the receptor
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Describe how InlB mediates entry.
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1) InlB binds to Met
2)Activates the Met receptor, leading to activation of intracellular signalling events 3) Inl-Met internalization is through clathrin machinery (clathrin mediated endocytocis) 4) Leads to signalling events, that cause activation of Arp2/3, WASP and cytoskeletal changes that induce entry |
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What type of bacteria use clathrin to mediate their entry into the host?
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Bacteria that use the zipper mechanism
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What happens to listeria entry if clathrin is KO?
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5fold decrease in bacterial entry
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Which Inl is required to cause infection in the blood brain barrier?
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InlB
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Which Inl is required to cause infection in the intestinal barrier?
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InlA
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Which Inl is required to cause infection in the placental barrier?
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Both can do this
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What receptor does InlA use in humans?
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E cadherin
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What is Vip?
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LPXTG anchored bacterial surface ptn
Vip is linked to p/g |
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What is gp96?
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Host ptn
ER chaperone ptn |
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How does bacterial Vip modulate the immune response?
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Vip binds gp96
Affects the trafficking of TLRs Vip also required for entry |
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What happens if Vip is deleted?
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Bacterial entry drops
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Describe the lysteriolysin O gene.
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SE: signal sequence
PEST: degradation signal IMH: transmb helix UND:undecapeptide (important for cholesterool binding) |
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How does listeria maintain its survival once it's in the phagosome?
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It escapes
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What is LLO (listeria lysin O)?
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Cholesterol dependent cytolysm
Responsible for lysis of the phagosome |
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What happens if LLO is deleted?
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Listeria becomes avirulent in vivo
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When does LLO become activated?
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When the pH in the phagosome drops below 6
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How does LLO work?
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When its activated, LLO oligomerizes to form a pore
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How long does it take listeria to escape out o the phagosome?
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~30 minutes after infection
By 2hrs after infection, 50% of the bacteria are in the cytoosol |
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What does host lysosomal thiol reductase do?
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Reduces LLO
Drives its oligomerization into a pore Pore cause Ca2+ release ->this prevents the recruitment of lysosomal ptn LAMP-1 -> This prevents maturation of phagosome to phagolysosome |
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What do PI-PLC and PC-PLC do?
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PI-PLC acts on phosphotidylinositol
PC-PLC acts on phosphatidyl choline PI/PC-PLC work in conjunction with the bacterial LLO to help get bacteria out of the phagosome |
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What else are these phospholipases used for?
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To get out of the vacuole after infecting another cell
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Describe the ActA gene.
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SS: signal sequence
A: acidic stretch AB: actin monomer binding region C: cofilin homology sequence LR (3X): long repeats TM: transmb domain black boxes: proline rich repeats |
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What happens once bacteria excape into the cytosol?
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Become motile
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How do these cells become motile?
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Hijack the host actin-cytoskeleton (does NOT make flagella)
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What are some other bact/microorgs that can form actin tails within the host?
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Ricketsia
Shigella flexneri Somes viruses can do this (Vaccinia) |
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What does ActA mimic?
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Host ptn WASP
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Describe what ActA does/ recruits and which regions it uses to do this.
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C-terminal region linked to bact cell wall
N-terminal region recruits host actin nucleating tn Arp2/3 Recruits VASP through proline rich region Actin polym occurs at bacterial end |
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What happens to bacteria that are ActA mutants?
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Impaired in cell attachment and entry
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What does actin polym induce?
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Comet-tail formation
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How does listeria spread from cell to cell?
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Motile bacteria contact the cell mb forming bacteria containing pseudopods
Bacteria is engulfed by neighboring cell Newly infected cell has double mb enclosed bacteria |
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What is require for the bacteria to get out of thise double mb phagosome?
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LLO and PLCs
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What is this mechanism of cell to cell spread important for?
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Evading host immune system and other extracellular bactericidal cmpds
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How many genes are required for listeria intracellular growth?
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41
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What are these genes for?
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Alternative Carbon utilization paths
Cell division Virulence Cell wall structure |
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What is the hexose phospohate transporter for?
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Its a glucose phosphate homolog
Required for intracellular replication Used to transport glucose-1-PO4, a nutrient in the host cytoplasm Required for bacterial proliferation in mouse organs |
