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94 Cards in this Set
- Front
- Back
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How many Pseudomonas species are there?
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~140 (know by rRNA studies)
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General characteristics of Pseudomonads?
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G-
Rod shaped Polar flagellum Motile Gamma proteobacteria Very diverse genus Metabolic capabilities Mostly aerobic (some facultative anaerobes) Diverse ecological niches Imp role in nature's C and N cycle |
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What is a characteristic feature of Pseud.?
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fluorescent siderophore production
Pigment production |
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What kind of pathogen is Pseud?
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Plant
Animal Human |
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What does P. fluorescens do?
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Plant growht properties
Plant pathogen control (biocontrol) |
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What does P. putida do?
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Degradation of polycyclic hydrocarbon (bioremediation)
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What does P. syringae do?
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Plant pathogen (tomatoes, tobacco)
Ice-nucleation properties cause frost damage |
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What does P. stutzeri do?
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Degradation of aromatic compunds, carbon tetrachloride (a CFC), crude oil and other hydrocarbons, biocides, metal cycling
(bioremediation) |
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P. aeruginosa general characteristics:
G+/- Shape? Motile? Lives? Spore? Fermentation? Tests it's positive for? Pigment production? |
G-
Rod Motile (polar flagellum) Ubiquitous in soil and water NON-spore forming Non-fermenting Tests: Oxidase +, Beta hemolytic Grows on laboratory medium and blood agar Pigment: Blue (pyocyanin), Yellow (pyoverdin), Brown (pyomelanin) |
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Where can P. aeruginosa colonize?
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Different ecological habitats
Can contaminate water sources, medical equpment (can cause disease) |
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What O2 env't does it like?
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facultative anaerobe
(NO3 is terminal acceptor) |
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What kind of metabolism does P. aeruginosa have?
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highly diverse
Minimal nutritional requirements Growth on many dicerse organic cmpds |
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Optimal growth of P. aeruginosa?
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37 degrees
but can grow btw 15-42 degrees =>Versatile physiology |
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Tolerance to env't stimuli?
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V/ tolerant to env't and physiological stresses
ex: osmolar, pH, metals, weak antiseptics, starvation |
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Colony morphology?
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Depends where its being isolated from
Distinctive phenotypic variants (mucoidy w/ alginate over production, small colony variants, pigment overproduction/loss, autolysis) |
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What kind of a pathogen is P. aeruginosa?
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Opportunistic
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Who does P. aeruginosa cause disease in?
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Compromised hosts
->immuno-suppression, compromised mucosal barrier, damaged tissues Nearly alll tissues and organs can be affected 4th most common nosocomial (hospital acq'd infection) pathogen (10%) |
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What kind of infection can P. aeruginosa cause?
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Acute
Subacute Chronic |
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Example of acute infections caused by P. aeruginosa?
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Nosocomial pneumonia
Corneal infection Bacteremia and sepsis |
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Example of subacute infections by P. aeruginosa?
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Soft tissue, skin infection
UTI Bone and joint infection |
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Examples of P. aeruginosa chronic infections?
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Chronic airway infection (CF)
Sinusitis Otitis media |
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What are virulence factors important for?
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Pathogenesis of acute and subacute infections
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What are virulence factors involved in?
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Tissue colonization
Cell/tissue damage Invasion and dissemination Activation of local and systemic inflammatory responses |
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What defines the type of virulence factors ass't with the bacteria?
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Host model systems
-Plant model -Amoeba -Nematode -Insects -Verterates |
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What kind of virulence factors are there?
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Exotoxins
LPS Type III secretion systems and effector ptns Flagellum, Type IV pili, non-pilus adhesins Pyocyanin, siderophores, rhamnolipids, HCN Protease, elastase, lipase, phospholipase |
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Whats the first step require for cells associate virulence factors?
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Adherence to epithelial cellls
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How does P. aeruginosa's virulence factors bind epithelial cells?
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Usually mediated by Type IV pili
-distal end contcts various surfaecs in a non-specific way (inert surfaces) or receptor specific way (galactose or mannose binding ptns to glycosphingolipids) on mammalian host cell surfaces |
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How does P. aeruginosa draw itself cloer to the host after it attaches?
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Retracts pilus
Mediates twitching (surface) motility |
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What part of P. aeruginosa can bind mucin in host?
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Flagellar cap ptn ( P. aeruginosa has a single polar flagellum)
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Describe LPS (cell ass't virulence factor)
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Endotoxin
Embedded in OM LPS can be a ligand to bind CFTR and enter epithelial cells This response might be protective (engulf and destroy)or pathogenic depending on cell type |
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Does the O-ag of LPS cause a protective response in the host?
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Probably not, even though it is highly immunogenic
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What does the Lipid A region of LPS do?
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Induces prod'n of inflammatory cytokines
-> mainly through CD14 and TLR4 mechanisms |
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What happens if too much TNF-alpha and IL-1 is released?
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Septic shock
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What can secreted extracellular virulence factors do?
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Cause tissue damage
Invasion Dissemination |
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What are examples of secreted extracellular virulence factors of P. aeruginosa?
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Alkaline protease
Protease V Exotoxin A Elastases LasA and LasB Phospholiase C Lipase LipA and LipC |
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What do Alkaline protease and protease IV do?
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Degrade complement components and cytokines
Hydrolyzes fibrin and fibrinogen |
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What does Exotoxin A do?
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Enter euk cells by receptor mediated endocytosis
Catalyzes ADP-ribosylation and inactivation of EF-2 .: inhibits ptn biosynthesis and causes cell death -Causes local tissue damage, bacterial invasion, can impair host defenses |
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What do Elastases Las A and Las B do?
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Destroy elastin (imp in lung tissue and bld vessels), fibrin and collagen, human surfactant, IgG/IgA
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What does phospholipase C do?
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Cleaves phospholipids
Induces release of inflammatory cytokine Vascular permeability and tissue damage |
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What do lipases LipA and LipC do?
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Degrade phospholipid (imp in lung surfactant)
Induce inflammatory cytokines (lipases are highly immunogenic) |
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Describe how the Type III secretion system and its effector ptns work.
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Exoptns secreted through T3SS
->require close contact with target cells to be toxic -T3SS injects its effector ptns directly into the target cells |
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What type of infections is T3SS responsible for?
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ACUTE infections
-> Kills host quickly ->invasive infections more than subacute or chronic infections |
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What are the 4 exoenz/toxins belonging to T3SS?
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Exoenz S
Exoenz T Exotoxin U Exotoxin Y |
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What do exoenzymes S/T do?
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ADP-ribosyltransferase that disrupts actin filaments, intracellular GTP-binding ptns
May impair wound healing and tissue repair Induce inflammation |
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What does exotoxin U do?
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Highly cytotoxic to mammalian cells
Likely due to phospholipase activity that destroys eukaryotic cell mbs |
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What does exotoxin Y do?
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Unknown
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When do T3SS cause chronic infections?
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When the T3SS is mutated
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Why does the bacteria have such a wide range of tools of infection at its disposal?
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Doesn't always want to kill the host (i.e. in mutant T3SS)
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Extracellular virulence factors
Rhamnolipids. |
Rhamnose-containing glycolipids biosurfactant with detergent like properties
Can dissolve lung surfactant May be important in biofilm formation Cytotoxic to PMNs |
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Extracellular virulence factors
Pyocyanin |
Redox active phenazine pigment that generates ROS
->Causes oxidative stress to host cells -> Can induce inflammatory response and apoptosis of neutrophils |
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Extracellular virulence factors
HCN (hydrogen cyanide) |
Cytochrome oxidase inhibitor
Causes arrest of mitochondrial respiration Causes death of C.elegans Unclear role in human infection |
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Extracellular virulence factors
Siderophores: Pyoverdin and pyochelin |
Iron scavengers
Compete with transferrin for iron Iron metabolism regulates expression of other virulence factors, bacterial growth and motility |
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Extracellular virulence factors
Exoplosaccharide and alginate |
Important in biofilm formation
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What is quorum sensing/
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Mode of bacterial communication
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Where was quorum sensing first seen?
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in V. fischeri (symbiont)
->at high cell density, bacterial cells re luminesent through expression of lux genes |
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How is QS (quorum sensing) mediated in P. aeruginosa and most other G- bact?
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Acyl-HSL (homoserine lactone) molecules
-> Auto inducers |
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How are acyl-HSL produced?
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LuxI-like ptn
When bound to their cognate transcription activator LuxR-like ptn, LuxR activates the transcription of many target genes |
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Describe QS.
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Low density: don't turn on genes
When reaches quorum (critical mass), turns on genes Cell has synthetases that are LuxI-like ptns ->synthesizes signals that diffuse out into the env't -After reaching a certain density, bind to LuxR-like receptors ->Induce T on target genes (after reach a critical density, turn on genes) |
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What are the 2 acyl-HSL signals in P. aeruginosa?
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3-oxo-C12-HSL (LasI-LasR system)
C4-HSL (RhII-RhIR ststem) (there's also a third non-acyl-HSL system that has the PQS signal: pseudomonas quinolone signal) |
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What does the QS result in
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Coordinated expression of virulence genes (among others) at high cell density that is growth phase dependent
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How many genes in Psuedomonas aeruginosa are regulated by QS?
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~350 (6%)
This includes virulence factors genes (encoding elastase, rhamnolipids, pyocyanin......) |
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What does the massive attack model explain?
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As single cells (low density), bacteria can't cause disease
However, expression of their virulence factors can alert the host defense/immune system .: virulence factors are only induced when bacteria has reached a critical density (As cell density increases, target gene expression inc as well) In best interest of bacteria to lay low and replicate, without alerting host ->Turn on virulence factors all at once when reach a critical mass so that you can have a longer effect |
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Why can QS modulate the inflammatory response?
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Subvert host responses and cause persistent infection
(ex: 3-oxo-C12-HSL can inhibit IL-12 prod'n from T cells and modulate away from a Th1 response. It cam also inhibit TNF-a (monocytes) and NF-kB signalling) BUT, 3-oxo-C12-HSL can also induce inflammation by inducing IL-8 in airway epithelial cells |
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What is another role of QS?
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Biofilm formation (critical to persistent chronic infections, particularly in CF patients)
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What is cystic fibrosis(CF)?
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Autosomal recessive disease
Caused by mutation in CFTR gene (encodes a transmb chloride channel) Most common Caucasian genetic disease (1/3000 ppl) |
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How is CF related to P. aeruginosa?
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Most CF patients are chronically infected with
->modeldisease for chronic P. aeruginosa infections |
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What do CFTR mutations cause?
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Abnormal NaCl transport across the epithelium
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What is the most common mutation in CFTR?
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dF508 mutation
->Causes abnormal trafficking of the CFTR ptn (ptn is there, but doesn't reach the surface, because it is targeted and destroyed) |
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What do mutations in CFTR end up causing (due to abnormal NaCl transport)?
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Thick and dehydrated mucus in airways, GI tract and other exocrine organs
->affects multiple organs, but nowadays, the main cause of disease and death is lung disease |
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When are ppl with CF infected with P. aeruginosa?
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At an early age
They become chronically infected with P. aeruginosa eventually This chronic infection causes destruction of the lungs and can cause death |
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What is the difference btw an intermittent P. aeruginosa infection and chronic infection?
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Intermittent:
- Low bacterial burden - Normal Lung fct - Bacterial phenotype similar to environmental strains - Can be cleared by early aggressive antibiotic treatment Chronic: -up to 10^10 bacteri/mL, -DECREASED lung fct, -bacteria have adapted to the CF lung env't -Cannot be eradicated by antibiotic treatment |
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What's the main difference between a chronic and intermittent P. aeruginosa infection?
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In chronic infection, can't be treated
Bacteria never completely go away, even if given antibiotics Need to cstly take antibiotics |
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What is a key reason for bacterial persistence in CF patients?
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Biofilms
-Clusters of bacteria embedded in a matrix |
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Why are biofilms so important in bacterial persistance?
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Form of bacterial resistance to antibiotics and host defenses
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Where does P. aeruginosa form biofilms in CF patients?
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In the sputum of their airways
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What is a biofilm?
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Structure communities of bacterial cvells growing to high densities, encased in an extracellular matric
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Where do biofilms attach?
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Attach to a surface
They are ubiquitous in the natural env't |
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What does the biofilm extracellular matrix consist of?
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Secreted polysacs, ptns, DNA, bacterial and host cellular debris
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What kind of diseases are caused by biofilm infections?
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Corneal infections
Peridontal disease Sinusitis and otitis media Endocarditis Endobronchial infections in patients with CF Prosthetic device and catheter-ass't infections |
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Why are chronic and subacute infections difficult to treat?
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Long, aggressive antibiotic treatment
Need to remove the infected tissue and/or foreign body May be impossible to eradicate (ex: chronic airway infection in CF patients) --> Seen with a wide range of bacteria: staph, strep, E. coli, NTHi |
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How do biofilms form?
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Individual cells attach to the surface and remain immobile
Bacteria divide to form aggregates, secrete polysac and form an extracellular matrix Aggregates grow and mature: change cellular metabolism and gene expression, cell-to-cell communication (QS), sub-specialization of the bacterial population, disintegratioin and release of cells (get a heterogenous population of genes, since dif genes are expressed in a biofilm than under other circumstances) |
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What does biofilm growth require (based on in-vitro studies)?
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QS
Iron Type IV pilus for surface attachment and motility Exopolysac production, including alginate |
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What are the benefits of a biofilm for the bacteria?
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At high cell density, cell-to-cell communication allow bacteria to regulate genes differently than at low density (virulence and toxins)
Cell physiology and metabolism change and allow the bacteria to withstand more stresses Bacterial population differentiates phenotypically and genetically into specialized sub-population |
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What is the difference btw acute and chronic infections?
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Acute: Invade ad disseminate, but are more susceptible to host defense and antibiotics
Chronic: Localized and persits, but are more resistant to host defenses (won't cuase septicemia) |
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How are biofilms less invasive than plaktonic bacteria?
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Biofilms: bacteria are encased in tenacious matrix
-> may limit spread of bacteria -> encased bacteria may provoke less inflammation Invasion and motility genes are turned off in biofilms (Damper acute virulence, create niche to replicate in) |
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What happens once bacteria form a biofilm?
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Bacteria are protected from the host's immune response
->Greater resistance to oxidants (such as NO and peroxidase) and AMPs -> More difficult to phagocytose, do not activate PMNs as much as planktonic bacteria -> PMNs can be immobilized by the biofilm matrix and host cells have difficulty penetrating its structure -> Ab can be trapped in the biofilm matrix and fail to mediate opsonic killing |
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Can Ab kill biofilm bacteria?
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No
Even at very large Ab doses, can't kill them off completely (A significant fraction of biofilm bacteria are not killed by antibiotics) ->This is because bact in a biofilm are heterogenous, .: some cells different from others |
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How are biofilms physiologically heterogeneous?
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Biofilm growth produces gradients in nutrients, oxygen and metabolic waste
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What is ana important bacterial nutrient?
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Fe
Important to biofilm formation at several stages for dev'p -> Bacteria are starving for iron within biofilms |
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Do biofilms produce genetic variants?
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Yes
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Describe the genetic variants in biofilm growth.
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CF patients are often infected with multiple genetic variants (morphotypes)
In-vitro biofilm growth also generates genetic varients at a high frequency Increased genetic diversity due to oxidative stress, endogenous to biofilm growth generating DNA breaks |
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What is the benefit of this diversity?
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Confers strength to bacterial populations and contribute to persistence
-> Diverse populations have a greater chance of survival than homogenous populations ->Will have some resistant strains |
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Summary
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P. aeruginosa is an opportunistic pathogen
Highly versatile Multiple virulence factors important in the pathogenesis of acute and subacute infections Complex regulation of virulence factors through a QS system and integration of multiple regulators CF chronic airway disease presents an important and unique paradigm of chronic infection Biofilm growth presents a different paradigm of infection pathogenesis and is o chronic infections |
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P. aeruginosa: pathogenic?
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Not meant to be a pathogen, but they are when they come into contact with humnand
Probably behaves differently in nature |
