Lecture 17 - Pseudomonas

Question 1

Classification?

Answer 1

Gram-negative rod-shaped

Question 2

Motility?

Answer 2

Single polar flagella (swimming motility), Type IV pili (twitching motility)

Question 3

Where is it found outside of hosts?

Answer 3

Ubiquitous: soil, water, on plants, survive upto 42C

Question 4

What percentage of people does it infect (not sick)?

Answer 4

Colonizes 4-12% of healthy people without making sick

Question 5

Where do infections usually occur?

Answer 5

Hospitals (nocosomial)

Question 6

When can it become dangerous?

Answer 6

Opportunistic pathogen – usually infects people with compromised
immune systems – elderly, AIDS patients, burn victims, cancer
patients undergoing chemotherapy, cystic fibrosis (CF) patients

Question 7

Which tissues can Pseudomonas infect?

Answer 7

Can infect virtually all tissues: causes endocarditis, pneumonia,
infections of the urinary tract, central nervous system, wounds, eyes,
ears, skin, and musculoskeletal system

Question 8

What diseases does Pseudomonas cause?

Answer 8

Eye infections in contact lens wearers, wound infections
in burn patients, chronic lung infections in CF patients, meningitis,
sepsis

Question 9

Major virulence factors?

Answer 9

Adhesins, secretion systems and toxins, biofilm formation

Question 10

Which adhesins does Pseudomonas have? What do they bind?

Answer 10

Type IV pili (asialoGM1), LPS (TLR4, CD14, CFTR), flagella (TLR5, TLR2, asialoGM1)

Question 11

Which secretion systems does Pseudomonas have? Sec dependent or independent? What do they secrete?

Answer 11

• 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

Question 12

What is alginate?

Answer 12

A mucoid exopolysaccharide released in biofilms, protects the bacteria from phagocytosis, attenuates
the host immune response; antibiotic resistance

Question 13

How are extracellular toxins secreted? What are the extracellular toxins secreted by Pseudomonas?

Answer 13

By the Type I and Type II systems into the extracellular

space. Alkaline Protease, ExoA, LasB (elastase), phospholipase C, pyocyanin.

Question 14

How are intracellular toxins secreted? What are the intracellular toxins secreted by Pseudomonas?

Answer 14

By the Type III “injectosome” system directly into host cells. ExoS, ExoT, ExoU, ExoY.

Question 15

What is ExoA?

Answer 15

ADP-ribosyltransferase (ADPRT) - a diphtheria-like toxin - gets endocytosed into host
cells and inhibits elongation factor 2 (eEF-2) ® inhibits protein translation ® cytotoxic

Question 16

What is LasB?

Answer 16

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

Question 17

What is phospholipase C?

Answer 17

Targets eukaryotic membranes, degrades surfactant lining lungs

Question 18

What is pyocyanin?

Answer 18

Redox active, pro-inflammatory, pro-apoptotic, cytotoxic pigment

Question 19

What are ExoS and ExoT?

Answer 19

ADP-ribosyltransferases – GTPase-activating, interrupt cell signaling, cause
apoptosis. Different targets?

Question 20

What is ExoU?

Answer 20

Phospholipase (like phospholipase C) - disrupts cell membranes, involved in sepsis, v. toxic

Question 21

What is ExoY?

Answer 21

Adenylate cyclase (like B. anthracis EF)

Question 22

What is alkaline protease?

Answer 22

Degrades fibrin (involved in blood clotting)

Question 23

What are biofilms made of?

Answer 23

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

Question 24

Where do biofilms usually form?

Answer 24

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.

Question 25

What is quorum sensing?

Answer 25

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.

Question 26

What is the significance of quorum sensing?

Answer 26

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

Question 27

What are autoinducers?

Answer 27

Acyl homoserine lactones

(AHLs) - also called HSLs for homoserine lactones

Question 28

Which genes are regulated via quorum sensing?

Answer 28

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

Question 29

What autoinducers are involved in las and rhl regulatory circuits?

Answer 29

AHL, 3-oxo-C12-HSL, C4-HSL

Question 30

What are the three main components of Pseudomonas QS systems?

Answer 30

Regulator/receptor/transactivator, autoinducer synthetase and the autoinducer.

Question 31

What is cystic fibrosis caused by?

Answer 31

Cystic fibrosis
transmembrane conductance regulator
(CFTR). CFTR mutations
disrupt the sodium and chloride ion balance and
hence the water flow across membranes.

Question 32

What is CFTR?

Answer 32

Chloride channel

Question 33

Why is CF dangerous?

Answer 33

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.

Question 34

What are adaptive phenotype changes in CF Pseudomonas?

Answer 34

1. Loss of flagella and virulence factors,
2. The switch to an aggregative lifestyle,
3. Rewiring and adaptation of the cell
   physiology and metabolism,
4. Acquisition of mechanisms that confer
   full antibiotic resistance.