GBTC 5212 Exam 3 (Pseudomonas aeruginosa)

What are pseudomonads?

Ubiquitous, non-fermentative, Gram-negative rods

Where are pseudomonads found?

Soil, water, decaying matter, hospitals

What metabolism do pseudomonads have?

Obligate aerobes

How can pseudomonads grow anaerobically?

Using nitrate or arginine as an electron acceptor

What are the three medically important genera of pseudomonads?

• Pseudomonas

• Burkholderia

• Stenotrophomonas

What species of Pseudomonas is clinically important?

aeruginosa

What species of Bulkholderia is clinically important?

cepacia and pseudomallei

What species of Stenotrophomonas is medically important?

maltophilia

What is Pseudomonas aeruginosa?

Medically important Gram-negative opportunistic pathogen

Why is Pseudomonas aeruginosa medically important?

• Increasing antibiotic resistance

• Arsenal of virulence factors

What is the primary method for identifying Pseudomonas aeruginosa?

Green pigmented colonies

What are some cell-associated virulence factors associated with Pseudomonas aeruginosa?

• Flagellum

• Alginate

• Pili

• Lipopolysaccharide

What are some extracellular virulence factors associated with Pseudomonas aeruginosa?

• Exotoxin A

• Siderophores

• Proteases

• Phospholipase C

• Exoenzyme S

• Exoenzyme U

• Rhamnolipids

• Pyocyanin

What is the alginate capsule?

Polymer of mannuronic and guluronic acid

What is another name for the alginate capsule?

Glycocalyx

What is the function of the alginate capsule?

• Suppresses the activity of lymphocytes and neutrophils

• Protection from phagocytosis

• Functions in attachment to epithelial cells

• Plays a role in the resistance to some antibiotics

• Scavenges reactive oxygen species (free radicals)

• Provides extracellular matrix for biofilm formation

What is the role of alginate lyase?

Controls the dispersal of Pseudomonas aeruginosa colonies when environmental conditions change

What is another name for lipopolysaccharide?

Endotoxin

What is the role of lipopolysaccharide?

Component of Gram-negative cell wall

What is the toxic portion of lipopolysaccharide?

Lipid A

What does Lipid A induce during Pseudomonas aeruginosa septicemia?

Septic shock

How is Lipid A toxic?

Cytokine storm by over-activating the Toll-like receptor 4 (TLR4) signaling pathway

What is a cytokine storm?

Massive, uncontrolled release of pro-inflammatory cytokines such as TNF-α, IL-6, and IL-1β

What can a cytokine storm cause?

• Systemic inflammation

• Organ failure

• Septic shock

What is the role of the pilus?

Attachment to epithelial cells

What is the pilus aided by?

Neuraminidase

What is the role of neuraminidase?

Removes the sialic acid residues from the pilus receptor on the eukaryotic cell

What is Exotoxin A?

ADP-ribosyl transferase enzyme similar to diphtheria toxin

What is the mechanism of Exotoxin A?

ADP-ribosylates elongation factor-2

What does Exotoxin A cause?

Inhibition of protein synthesis process causing cell death (apoptosis)

What are T3SS effector proteins?

• Exoenzyme S

• Exoenzyme T

• Exoenzyme U

• Exoenzyme Y

How are T3SS effector proteins transmitted?

Injected directly from cytoplasm into the host cell

What is the mechanism of T3SS effector proteins?

Rearrangement of actin filaments in the eukaryotic cell

What is the effect of T3SS effector proteins?

Epithelial cellular damage and necrosis

What selects against T3SS effector proteins?

Chronic lung infections in CF and COPD

Why is T3SS not found in chronic lung infections?

It is highly immunogenic and associated with acute infection.

What are the components of elastase?

• LasB

• LasA

What is LasB?

Zinc metalloprotease

What does LasB destroy?

• Blood vessels

• Skin

• Lungs

• IgG and complement components

Why does LasB target the lungs?

The lungs are 30% elastin

What is LasA?

20-kDA extracellular zinc metallopeptidase

What is another name for LasA?

Staphylolysin

What is the role of LasA?

Synergizes with LasB in destroying elastin in tissues

What is the role of alkaline protease?

Destroys tissues, inactivates and destroys cytokines

What does alkaline protease specifically degrade?

• Complement proteins (C2, C3, and C1q)

• Monomeric flagellin

• Cytokines (IFN and TNF)

What is the purpose of degrading complement proteins?

Preventing bacterial lysis

What is the purpose of cleaving monomeric flagellin?

Evading TLR5 immune detection

What is the role of protease IV?

Associated with keratitis

What is the role of phospholipase C?

Degrades phospholipids in eukaryotic cells to induce inflammatory response

What are rhamnolipids?

Glycolipid surfactants

What is the role of rhamnolipids?

• Disrupts lecithin-containing tissues

• Facilitate surface motility (swarming)

• Develop and disperse biofilms

• Enhance nutrient uptake

• Reduce surface tension

• Emulsify hydrophobic substrates

• Suppress host immunity and exhibit antimicrobial activity

What is the role of pyocyanin?

• Blue pigment

• Induces tissue damage through the release of toxic oxygen radicals

• Enhances the release of IL-8

What is cystic fibrosis?

Autosomal recessive disease

What is the incidence of cystic fibrosis?

1 every 3,200 Caucasian births

What is the median life expectancy of cystic fibrosis patients?

33 years

What are the characteristics of cystic fibrosis?

• Salty sweat

• Intestinal obstruction

• Pancreatic insufficiency

• Severe pulmonary disease

What is the cause of cystic fibrosis?

Defective cystic fibrosis transmembrane regulator (CFTR)

What kinds of pulmonary disease are caused by cystic fibrosis?

• Chronic microbial colonization

• Repeated acute exacerbations

• Spectrum of pathogens (Pseudomonas aeruginosa)

What is the most common cause of death in cystic fibrosis patients?

Respiratory failure due to gradual loss of lung function

How does Pseudomonas aeruginosa adapt to the hypoxic cystic fibrosis lung environment?

Denitrification

What is denitrification?

Using nitrate and nitrite as alternative terminal electron acceptors for anaerobic respiration

What Pseudomonas aeruginosa is associated with chronic biofilms in cystic fibrosis lungs?

OprF

What is OprF?

Outer membrane protein F

What does OprF do?

• Limits membrane permeability

• Reduces antibiotic uptake

• Aids in escaping phagocytosis

What is folliculitis caused by?

Immersion in contaminated water

What is external otitis?

Swimmer's ear

What is BCC?

Burkholderia cepacia complex

Where is BCC found?

Soil and water

How is BCC transmitted?

• Person-to-person contact

• Contact with contaminated surfaces

• Exposure in the environment

• Contaminated medicines and devices

What are the clinical effects of BCC?

• Usually a colonizer, it causes no symptoms at all in immunocompetent persons

• Those with weakened immune systems or chronic lung diseases are susceptible

• Serious respiratory infections occur, especially in patients with cystic fibrosis, bronchiectasis, chronic granulomatous disease, in whom morbidity and mortality is highest

Why is BCC infection so hard to treat?

They are often resistant to common antibiotics and most commonly affect immunocompromised patients