Lecture 17 - Pseudomonas Flashcards
Classification?
Gram-negative rod-shaped
Motility?
Single polar flagella (swimming motility), Type IV pili (twitching motility)
Where is it found outside of hosts?
Ubiquitous: soil, water, on plants, survive upto 42C
What percentage of people does it infect (not sick)?
Colonizes 4-12% of healthy people without making sick
Where do infections usually occur?
Hospitals (nocosomial)
When can it become dangerous?
Opportunistic pathogen – usually infects people with compromised
immune systems – elderly, AIDS patients, burn victims, cancer
patients undergoing chemotherapy, cystic fibrosis (CF) patients
Which tissues can Pseudomonas infect?
Can infect virtually all tissues: causes endocarditis, pneumonia,
infections of the urinary tract, central nervous system, wounds, eyes,
ears, skin, and musculoskeletal system
What diseases does Pseudomonas cause?
Eye infections in contact lens wearers, wound infections
in burn patients, chronic lung infections in CF patients, meningitis,
sepsis
Major virulence factors?
Adhesins, secretion systems and toxins, biofilm formation
Which adhesins does Pseudomonas have? What do they bind?
Type IV pili (asialoGM1), LPS (TLR4, CD14, CFTR), flagella (TLR5, TLR2, asialoGM1)
Which secretion systems does Pseudomonas have? Sec dependent or independent? What do they secrete?
- Type I secretion system (Sec independent): alkaline
protease - Type II secretion system (Sec dependent):
elastase (LasB), phospholipase,
exotoxin A (ExoA), pyocyanin - Type III secretion system (Sec independent):
exotoxins ExoS, U, T, Y
What is alginate?
A mucoid exopolysaccharide released in biofilms, protects the bacteria from phagocytosis, attenuates
the host immune response; antibiotic resistance
How are extracellular toxins secreted? What are the extracellular toxins secreted by Pseudomonas?
By the Type I and Type II systems into the extracellular
space. Alkaline Protease, ExoA, LasB (elastase), phospholipase C, pyocyanin.
How are intracellular toxins secreted? What are the intracellular toxins secreted by Pseudomonas?
By the Type III “injectosome” system directly into host cells. ExoS, ExoT, ExoU, ExoY.
What is ExoA?
ADP-ribosyltransferase (ADPRT) - a diphtheria-like toxin - gets endocytosed into host
cells and inhibits elongation factor 2 (eEF-2) ® inhibits protein translation ® cytotoxic
What is LasB?
A Zn2+ metalloprotease, degrades elastin (a connective tissue protein) and
complement protein C3, breaks down tight junctions to increase the permeability of the
respiratory epithelium
What is phospholipase C?
Targets eukaryotic membranes, degrades surfactant lining lungs
What is pyocyanin?
Redox active, pro-inflammatory, pro-apoptotic, cytotoxic pigment
What are ExoS and ExoT?
ADP-ribosyltransferases – GTPase-activating, interrupt cell signaling, cause
apoptosis. Different targets?
What is ExoU?
Phospholipase (like phospholipase C) - disrupts cell membranes, involved in sepsis, v. toxic
What is ExoY?
Adenylate cyclase (like B. anthracis EF)
What is alkaline protease?
Degrades fibrin (involved in blood clotting)
What are biofilms made of?
Self-produced matrix of exopolysaccharide
(EPS: alginate, Pel and Psl) and extracellular
DNA (eDNA), which provides structure and
attaches them to organic (biotic) or inorganic
(abiotic) surfaces. Biofilms are complex
communities of cells that can be comprised of
one species or multiple species of bacteria
Where do biofilms usually form?
Any biotic or abiotic surface, particularly ones where there’s a nutrient flow
across the surface. They can form in anaerobic conditions. They can establish on teeth, contact
lenses, in-dwelling devices like catheters, joint prostheses, mechanical heart valves.
What is quorum sensing?
Complex bacterial cell-to-cell signaling
systems using autoinducers that allow the bacteria to sense their own cell density (i.e how many of us
are out there?) and respond appropriately by coordinating production of virulence factors.
What is the significance of quorum sensing?
Switch to a new metabolic program – eg. production of virulence factors – only when there are enough of them to be effective - the group can achieve much more than might be possible with only a few cells
What are autoinducers?
Acyl homoserine lactones
(AHLs) - also called HSLs for homoserine lactones
Which genes are regulated via quorum sensing?
In addition to virulence factors, QS can
signal antibiotic production (defense against
competing strains of bacteria), nutrient
acquisition, bioluminescence, pigment
production, etc. depending on the organism
What autoinducers are involved in las and rhl regulatory circuits?
AHL, 3-oxo-C12-HSL, C4-HSL
What are the three main components of Pseudomonas QS systems?
Regulator/receptor/transactivator, autoinducer synthetase and the autoinducer.
What is cystic fibrosis caused by?
Cystic fibrosis transmembrane conductance regulator (CFTR). CFTR mutations disrupt the sodium and chloride ion balance and hence the water flow across membranes.
What is CFTR?
Chloride channel
Why is CF dangerous?
Thick, sticky mucous in the lungs
and airways, digestive tracts, etc. that cannot be removed by cilia –
makes breathing difficult.
Bacteria like P. aeruginosa become trapped,
form biofilms, resulting in chronic lung
infections.
What are adaptive phenotype changes in CF Pseudomonas?
- Loss of flagella and virulence factors,
- The switch to an aggregative lifestyle,
- Rewiring and adaptation of the cell
physiology and metabolism, - Acquisition of mechanisms that confer
full antibiotic resistance.
