VL18a: Pseudomonas pathogenesis

Question 1

Characteristics of pseudomonas

Answer 1

• opportunistic pathogen of plants animals and humnans
• gram -, rod shaped
• soil bacteria
• large genome (high metabolic diverisity)
• obligate aerobe
• motile with polar flagella
• resistant to multiple drugs

Question 2

What kinds of infections is pseudomonas known for? /where does it infect?

Answer 2

• burn wounds
• lungs of CF patients
• eye (contact lenses)

has many virulence factors
forms biofilms
resistant to many antibiotics

Question 3

What has p.aeruginosa to do with burn wounds?

Answer 3

most common cause of burn wound infection

65% of fatal burn cases because of septicemia

Question 4

What does eschar mean?

Answer 4

dead tissue,- a moist, protein rich, avascular environment that encourages microbial growth
avascularity
restricts migration of immune cells and (systemically administered) antibiotics because of avascularity

Question 5

What is cystic fibrosis?

Answer 5

disorder of chloride channels (recessive mutation in CFTR-transmembrane conductance regulator)
leads to thick mucus in lungs
-opportunistic pathogen infections
-90% get chronic respiratory failure from infection

Question 6

Why/How does pseudomonas infect lungs of CF patients?

Answer 6

in CF mucus layer uniformly viscuous, mucus cant be propelled outward
CFTR-mutant protein also increases adhesion of P. aeruginosa to epithelium

Question 7

Pseudomonas eye infections

Answer 7

microbial keratitis
infection and inflammation usually in combination with contacts
can lead to scarring and vision loss

Question 8

Name 3 other types of infections pseudomonas can cause

Answer 8

UTI, bacteremia, endocarditis

Question 9

Give an overview over the viurlence factors pseudomonas has

Answer 9

cell associated factors:

• Adhesins (flagella, pili, lps. alignate(important in biofilm formation))
• MDR efflux pumps
• T3SS
• QS

Secreted toxins and enzymes

• Exotoxin A
• Exoenzymes
• Phospholipase C
• Proteases

Question 10

4 step QS review

Answer 10

dependen on location QS receives different signals, regulated different genes

1. AHL dependent QS important for many infections
2. P.aeruginosa uses HSL (hemoserine lactone) QS regulatory systems to control expression of many virulence factors
3. Interest of targeting QS for infection control
4. Unclear if HSL-regulated virulence plays the same role during acute and chronic infections

Question 11

How does the qurom sensing cascade work?

Answer 11

three QS systems that work together

1. primary system= Las system: LasI (produces HSL) and LasR (transcription regulator)
2. LasIR autoinduces and induces Rhl system (RhlI produces HSL (hemoserine lactone), RhlR receptor, autoinduction)
3. Pseudomonas quinolone signal (PQS) also regulates virulence gene expression

Question 12

What virulence factors are critical for establishing an infection?

Answer 12

Adhesins

Pili (type4), Polysaccharide capsule, alginate, lectins

Question 13

Which virulence factors help during invasion?

Answer 13

Proteases
Hemolysins/cytolysins
-secreted pigments (produce ROS, or as sideophores)
-Toxins
-T3SS

Question 14

Which virulence factors help in defence

Answer 14

• Rhamnolipid (surfactant, lysis of macrophages)

- alkaline protease (blocks complement activation in classical and lecitin pathway by cleavage of C2)

Question 15

Summary

Answer 15

• persistence of chronic Pseudomonas aeruginosa lung infections in CF patients is due to biofilm-growing mucois (alignate-producing) strains
• Biofilms cause chronic infections because of increased tolerance to anitbiotics, resistance to phagocytosis and other components of the innate and the adaptive immune system
• A pronounced antibody response develops, leading to immune complex mediated chronic inflammation, dominated by polymorphonuclear leukocytes. The chronic inflammation is the major caue of the lung tissue dammage in CF.
• Biofilm growth in CF lungs is associated with an increased frequency of mutations, slow groth and adaption of the B to lung conditions and to antibiotics. low bacterial metabloc activity and increase of doubling tiems of the bacterial cells in the lungs are responsible for some of the tolerance to antibiotics
• Conventional resistance mechanisms, such as chromosomal ß-lactamase, upregulated efflux pumps and mutations of antibiotic target molecules in the bacteria contribute to the sruvival of P.aeruginosa biofilms

Question 16

What does hydrogen cyanide do?

Answer 16

hcnABC
regulated by both QS systems
at high concentrations in patients with freshly infected burns
virulence factor (mutants have reduced virulence)
-Inhibits important metalloenzymes (cytochrome c oxidase, inhibits aerobic respiration)

Question 17

Why is drug resistance such a problem?

Answer 17

mutator bacteria
(B with high mutation rates, enriched under selection, patients are always treated with antibiotics, inactivation of mismatch repair increases muation rate)

drug efflux