General Characteristics
- Gram-negative bacilli
- Encapsulated
- Motile: 1–3 motile flagella
- Obligate aerobe
- Oxidase positive
- Catalase positive
- Non-lactose fermenting
- Produces a blue-green pigment: due to pyocyanin and fluorescein production
- Produces a characteristic fruity, grape-like odor
- Clinically relevant species: Pseudomonas aeruginosa (P. aeruginosa)
Photograph depicts the colonial growth pattern displayed by Pseudomonas aeruginosa bacteria.
Image: “6688” by the CDC/Dr. Theo Hawkins. License: Public domain.Related videos
Pathogenesis
Reservoir and transmission
Reservoir:
- Ubiquitous in the environment
- Moist reservoirs:
- Sinks
- Respiratory and dialysis equipment
Transmission:
- Person-to-person transmission from infected reservoirs
Risk factors
- Neutropenia
- Burn injuries
- Asplenia
- Cystic fibrosis
- Endotracheal intubation
- Chronic, indwelling catheters
Pathogenesis of P. aeruginosa
Virulence factor | Effect |
---|---|
Polysaccharide capsule |
|
Pili |
|
Phospholipase C |
|
Exotoxin A |
|
Pyocyanin |
|
Type III secretion system |
|
In vivo biofilm formation |
|
ꞵ-lactamase and efflux pumps |
|
Diseases Caused by P. aeruginosa
Type of condition | Characteristics |
---|---|
Urinary tract infection |
|
Burn wound infections | Associated with burn injuries, causing: |
Ear infections | Otitis externa:
|
Skin infections | Ecthyma gangrenosum:
|
Pulmonary infections |
|
Eye infections | Occurs in contact lens wearers or minor eye trauma:
|
Disseminated infections | Occurs in immunocompromised hosts:
|
Osteomyelitis |
|
Diagram of common sites of Pseudomonas infection
Image by Lecturio.Antimicrobials
Treatment
- P. aeruginosa has varying resistance to antibiotics:
- Multi-drug resistant: resistant to at least 1 agent in > 3 antibiotic categories
- Extensively drug resistant: resistant to at least 1 agent in all but 2 antibiotic categories
- Pan-drug resistant: resistant to all antibiotic categories
- Antibiotic choice is tailored to local resistance patterns (combination antibiotic therapy):
- 1st line:
- Combination penicillin/beta-lactamase inhibitors (piperacillin/tazobactam)
- Cephalosporins (ceftazidime)
- Monobactam (aztreonam)
- Fluoroquinolones (ciprofloxacin) (only oral)
- Carbapenems (meropenem)
- Multi-drug-resistant strains are treated with newly developed antibiotics:
- Beta-lactam-beta-lactamase inhibitor combinations (ceftolozane/tazobactam)
- Cephalosporins (cefiderocol)
- Carbapenem-beta-lactamase combination (imipenem-cilastatin-relebactam)
- Polymyxins
- Adjunct antibiotics: aminoglycosides (tobramycin, gentamicin, amikacin)
- 1st line:
Prevention
- Hygiene within the hospital:
- Use of appropriate sterile technique
- Careful cleaning of communal sinks and showers
- Periodic monitoring, replacement, and cleaning of:
- Respiratory support equipment
- Intravenous (IV) lines (especially long-term lines)
- Catheters
Mnemonic
To help remember the many clinically relevant facts about Pseudomonas, use the mnemonic “PSEUDOMONAS”:
- Pneumonia, pyocyanin
- Sepsis
- Ecthyma gangrenosum
- UTIs
- Diabetes, drug use
- Osteomyelitis
- Mucoid, polysaccharide capsule
- Otitis externa (“swimmer’s ear”)
- Nosocomial infections (catheters, endotracheal tubes)
- Exotoxin A
- Skin infections (“hot tub” folliculitis and burns)
References
- Riedel, S., & Hobden, J.A. (2019). In Riedel S, Morse SA, et al (Eds.), Jawetz, Melnick, & Adelberg’s Medical Microbiology (28th ed.)
- Hohmann, E.L., & Portnoy, D.A. (2018). In Jameson JL, et al (Eds.), Harrison’s Principles of Internal Medicine (20th ed. Vol 2, pp. 2676–2683).
- Baron, S. (1996). Medical microbiology. University of Texas Medical Branch at Galveston. https://www.ncbi.nlm.nih.gov/books/NBK7627/