Microbiology · MU Sofia

66. Genus Pseudomonas. Pseudomonas aeruginosa.

Covers the general characteristics of Pseudomonas aeruginosa, its epidemiology as an opportunistic hospital pathogen, and a table of virulence factors with their functions. It then describes pathogenesis, the range of diseases from respiratory, wound and burn, skin, eye and ear infections to urinary infections and sepsis, followed by diagnosis by sample, microscopy, culture and biochemical tests. The note closes with treatment based on sensitivity testing, synergistic antibiotic combinations, and infection control measures in hospitals.

Inside: 9 sections · 5 labelled pictures · 2 tables · 14 flashcards · 3 min

Topic 66 of 113 in the MU Sofia syllabus for Microbiology (Dental Medicine, Year 2). The free AceMed note covers it in 9 sections, about 285 words (3 min of reading), with 14 flashcards.

In this note

  1. Genus Pseudomonas. Pseudomonas aeruginosa
  2. General Characteristics
  3. Epidemiology
  4. Virulence Factors
  5. Pathogenesis
  6. Diseases Caused
  7. Diagnosis
  8. Treatment
  9. Prevention

General Characteristics

  • Gram stain: Gram-negative rods
  • Oxygen requirement: Obligate aerobes
  • Motility: Motile (polar flagella)
  • Non-fermenters: Do not ferment lactose or glucose (non-fermentative)
  • Oxidase: Positive
  • Catalase: Positive
  • Pigment production: Produces pyocyanin (blue-green) and pyoverdin (yellow-green)
  • Smell: Characteristic grape-like or fruity odor
  • Colony appearance: Flat, spreading colonies with metallic sheen on nutrient agar
  • Growth media: Grows well on nutrient agar, blood agar, MacConkey agar (non-lactose fermenter)

Epidemiology

  • Ubiquitous in nature — soil, water, hospitals (sinks, catheters, ventilators)
  • Opportunistic pathogen, especially in:
  • Immunocompromised patients (e.g. cancer, CF, burns)
  • Prolonged antibiotic use
  • Hospital environments (nosocomial infections)

Pathogenesis

  • Adheres to epithelium via pili
  • Forms protective biofilms (e.g., lungs in CF patients)
  • Releases toxins and enzymes that disrupt host cell membranes and immune defenses
  • Can survive in moist hospital environments and resist many disinfectants

Diseases Caused

1. Respiratory Tract:

  • Tracheobronchitis
  • Necrotizing bronchopneumonia (esp. in CF patients)

2. Wound and Burn Infections:

  • Blue-green pus
  • Rapid spread in immunocompromised or burn victims

3. Skin Infections:

  • Folliculitis (e.g., "hot tub rash")
  • Ecthyma gangrenosum (necrotic ulcer with central black eschar)

4. Eye:

  • Keratitis (especially contact lens users)
  • Endophthalmitis

5. Ear Infections:

  • Otitis externa ("swimmer’s ear")
  • Malignant otitis externa (in elderly diabetics)

6. Urinary Tract Infections:

  • Often catheter-associated

7. Bacteremia/Sepsis:

  • High mortality in immunocompromised

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