BACTERIA · Gram-negative rod (non-fermenter)
Pseudomonas aeruginosa
Pseudomonas aeruginosa — Pigment production on culture
Stain: Culture plate (blue-green pyocyanin pigment)Morphology: Aerobic gram-negative rod producing blue-green pigment with grape-like / fruity (corn tortilla) odorYield: HIGHDifficulty: MEDIUM
Image: Wikimedia Commons · File:Pseudomonas_aeruginosa_pigment_production.jpg · HansN. (CC BY-SA 4.0)
Key facts
**Pathogenesis**: Obligate aerobe — thrives in moist environments. Pyocyanin generates ROS damaging tissue; exotoxin A inhibits EF-2 (like diphtheria toxin); LPS endotoxin → shock. **Diagnostic clue**: Oxidase-positive, non-lactose fermenter, blue-green pigment (pyocyanin + pyoverdine), grape/corn-tortilla odor. **Virulence**: Biofilm/alginate capsule (CF lungs), phospholipase C, elastase.
Boards buzzwords
- blue-green pigment
- grape/fruity odor
- burn wounds
- hot tub folliculitis
- ecthyma gangrenosum
- swimmer's ear
- CF lung
Associated diseases
- Burn wound infections / sepsis
- Ventilator-associated pneumonia
- Cystic fibrosis lung colonization
- Otitis externa & malignant otitis externa in diabetics
- Hot tub folliculitis
- Ecthyma gangrenosum in neutropenic patients
Treatment
Anti-pseudomonal beta-lactam (pip-tazo, ceftazidime, cefepime, meropenem) + aminoglycoside or ciprofloxacin for serious infections; aztreonam if penicillin-allergic
Related organisms
Listeria monocytogenes
Gram-positive rod (facultative intracellular)
Mycobacterium tuberculosis
Acid-fast bacillus (mycolic acid cell wall)
Nocardia spp.
Gram-positive filamentous, partially acid-fast
Treponema pallidum
Spirochete
Mycobacterium leprae
Acid-fast bacillus (obligate intracellular)
Neisseria meningitidis
Gram-negative diplococci