Microbiology · Other Gram-negative rods
Pseudomonas aeruginosa !
- Bacterium
- Gram-negative
- Contact
- Exam priority: medium
A water and soil bacterium that attacks hospital, burn and cystic fibrosis patients, and resists many antibiotics.
Updated 2026-11-01
At a glance
- Gram
- Gram-negative
- Shape
- Rod
- Oxygen
- Strict aerobe
- Family
- Pseudomonadaceae
- Stain
- Gram: red rods
Morphology
- Motile Gram-negative rod with a polar flagellum
- Non-lactose fermenter (colorless colonies on MacConkey); oxidase-positive
- Blue-green (pyocyanin) and fluorescent yellow (pyoverdine) pigments; sweet grape-like smell
- Cystic fibrosis strains form mucoid colonies (alginate)
Transmission
- Contact with contaminated surfaces, equipment or hands in hospital
- Water: sinks, humidifiers, pools and hot tubs, contact lens solutions
- Puncture wounds of the foot and burns
- Contact (on top of standard) for multidrug-resistant strains
Reservoir: Water and soil; damp hospital environments
Isolation precautions
What the care team adds to standard precautions.
- Contact
- Gown and gloves; dedicated equipment. For C. difficile, soap-and-water hand washing.
Virulence factors
- Exotoxin A: inactivates elongation factor 2 (EF-2) and stops protein synthesis
- Type III secretion system (ExoS, ExoU): cell damage and necrosis
- Elastase, phospholipase C and pyocyanin: tissue destruction and oxidative stress
- Alginate biofilm: shields against antibiotics and host defenses, typical in cystic fibrosis
- Efflux pumps, porin loss and beta-lactamases: multidrug resistance
Diseases it causes
- Otitis externa (swimmer's ear) and malignant otitis externa in people with diabetes Otitis externa →
- Pneumonia, mainly hospital-acquired and ventilator-associated; in the community, in people with structural lung disease Community-acquired pneumonia →
- Foot osteomyelitis after a puncture through a shoe, and in people who inject drugs Osteomyelitis →
- Chronic lung infection in cystic fibrosis and bronchiectasis Bronchiectasis →
- Bacteremia and sepsis; ecthyma gangrenosum in neutropenic patients Sepsis and septic shock →
Clinical picture
- Hot tub folliculitis: itchy pustules that clear on their own
- Keratitis in contact lens wearers
- Burn infection with green discharge
- Catheter-associated urinary infection
Diagnosis
- Culture: non-lactose-fermenting, oxidase-positive colonies with green pigment and a grape smell
- Always test susceptibility: multiple resistance is common
Treatment
Antipseudomonal beta-lactams (piperacillin-tazobactam, ceftazidime, cefepime, or carbapenems other than ertapenem), fluoroquinolones (ciprofloxacin, levofloxacin) or aminoglycosides, guided by the antibiogram; critically ill patients sometimes get a combination at first. Multidrug-resistant strains may need newer combinations or colistin.
Drug class only; doses and regimens are set by the clinician from the current guideline.
In Pharmacology:
- Piperacillin + tazobactam
- Ceftazidime
- Cefepime
- Meropenem
- Ciprofloxacin
- Tobramycin
- Colistin (colistimethate)
Prevention
- Hand hygiene and cleaning of equipment and surfaces
- Removing catheters and ventilators as soon as possible
- Contact lens care and hot tub and pool water care
- Careful antibiotic use
Test yourself
Think of the answer, then tap the question to see it.
Which tests and colony traits suggest Pseudomonas aeruginosa?
Oxidase-positive, non-lactose fermenter, blue-green pigment and a sweet grape-like smell.
Which Pseudomonas ear infection is dangerous in people with diabetes?
Malignant otitis externa, which can invade the temporal bone.
How does exotoxin A work?
It ADP-ribosylates and inactivates elongation factor 2 (EF-2), stopping protein synthesis.
Which necrotic skin lesion appears in neutropenic patients with Pseudomonas bacteremia?
Ecthyma gangrenosum.
Why are cystic fibrosis strains hard to clear?
They form mucoid alginate biofilms that shield them from antibiotics and host defenses.
Related
Related conditions
← Back to the group: Other Gram-negative rods
Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: About Pseudomonas aeruginosa (CDC, 2025); Pseudomonas and Related Infections (MSD Manual Professional Edition, 2024); Antimicrobial resistance (WHO, 2026).
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Representative model, for educational purposes only.