Pseudomonas aeruginosa

Question 1

What are the key characteristics of P. aeruginosa?

Answer 1

Obligate aerobe (requires oxygen)
Non-lactose fermenting
Oxidase positive
Produces distinctive grape-like scent
Forms blue-greenish colonies on culture due to:
- Pyoverdine
- Pyocyanin pigments

Question 2

What are the key biochemical tests for identifying P. aeruginosa?

Answer 2

Oxidase test: Positive
Lactose fermentation: Negative
Aerobic growth: Required
Pigment production: Blue-green
Distinctive odor: Grape-like smell

Question 3

What are the three main toxins produced by P. aeruginosa?

Answer 3

1. Phospholipase C
2. Endotoxin
3. Exotoxin A (inhibits EF2 through ADP-ribosylation)

Question 4

How does Exotoxin A work?

Answer 4

Targets Elongation Factor 2 (EF2)
Uses ADP-ribosylation
Inhibits protein synthesis
Similar mechanism to diphtheria toxin

Question 5

What are the major clinical manifestations of P. aeruginosa infection?

Answer 5

1. Nosocomial infections
2. Otitis externa (ear infection)
3. Pneumonia
4. Osteomyelitis
5. Ecthyma gangrenosum (in immunocompromised patients)

Question 6

What is ecthyma gangrenosum?

Answer 6

Rapidly progressive necrotic cutaneous lesions
Characteristic of P. aeruginosa infection
Typically occurs in immunocompromised patients
Presents as black necrotic lesions

Question 7

Which patients are at highest risk for P. aeruginosa infections?

Answer 7

Hospital patients (nosocomial infections)
Immunocompromised individuals
Burn patients
Cystic fibrosis patients
Patients with invasive medical devices

Question 8

What are the key laboratory features for identifying P. aeruginosa?

Answer 8

1. Colony appearance: Blue-greenish
2. Distinctive grape-like odor
3. Pigment production:
   - Pyoverdine
   - Pyocyanin
4. Oxidase positive
5. Non-lactose fermenting

Question 9

What are the unique cultural characteristics of P. aeruginosa?

Answer 9

Growth requirements: Strictly aerobic
Colony color: Blue-green
Pigments: Pyoverdine and Pyocyanin
Odor: Grape-like scent
Growth pattern: Non-lactose fermenting

Question 10

Why is P. aeruginosa considered clinically important?

Answer 10

1. Major cause of hospital-acquired infections
2. Natural resistance to many antibiotics
3. Causes severe infections in immunocompromised patients
4. Can cause rapid tissue destruction
5. Associated with high mortality in certain populations.