[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Microbiology](https://durgical.com/en/microbiology/) › [Other Gram-negative rods](https://durgical.com/en/microbiology/groups/other-gram-negative-rods/) › Pseudomonas aeruginosa [Microbiology](https://durgical.com/en/microbiology/) · [Other Gram-negative rods](https://durgical.com/en/microbiology/groups/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 ## Key points - Oxidase-positive non-fermenter, green pigment and grape smell. - Burns, cystic fibrosis, ventilator, neutropenia: think Pseudomonas. - Malignant otitis externa in the patient with diabetes. - Osteomyelitis after a puncture wound through a sneaker. - Exotoxin A inactivates EF-2, like diphtheria toxin. - Needs a specific antipseudomonal drug; many common beta-lactams miss it. ## 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 →](https://durgical.com/en/conditions/otitis-externa/) - Pneumonia, mainly hospital-acquired and ventilator-associated; in the community, in people with structural lung disease [Community-acquired pneumonia →](https://durgical.com/en/conditions/community-acquired-pneumonia/) - Foot osteomyelitis after a puncture through a shoe, and in people who inject drugs [Osteomyelitis →](https://durgical.com/en/conditions/osteomyelitis/) - Chronic lung infection in cystic fibrosis and bronchiectasis [Bronchiectasis →](https://durgical.com/en/conditions/bronchiectasis/) - Bacteremia and sepsis; ecthyma gangrenosum in neutropenic patients [Sepsis and septic shock →](https://durgical.com/en/conditions/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](https://durgical.com/en/pharmacology/piperacillin-tazobactam/) - [Ceftazidime](https://durgical.com/en/pharmacology/ceftazidime/) - [Cefepime](https://durgical.com/en/pharmacology/cefepime/) - [Meropenem](https://durgical.com/en/pharmacology/meropenem/) - [Ciprofloxacin](https://durgical.com/en/pharmacology/ciprofloxacin/) - [Tobramycin](https://durgical.com/en/pharmacology/tobramycin/) - [Colistin (colistimethate)](https://durgical.com/en/pharmacology/colistin/) ## 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 ## In Colombia It is one of the most frequent bacteria in healthcare-associated infections in Colombian intensive care units, which the INS tracks. ## Memory aid "Pseudomonas smells of grapes, paints things green and swims in every water": the hot tub, the contact lens, the swimmer's ear and the ventilator. ## 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. [Add to my cards (5)](https://durgical.app/estudiar/?add=/en/microbiology/pseudomonas-aeruginosa/) ## Related - [Acinetobacter baumannii](https://durgical.com/en/microbiology/acinetobacter-baumannii/) - [Klebsiella pneumoniae](https://durgical.com/en/microbiology/klebsiella-pneumoniae/) ## Related conditions - [Otitis externa](https://durgical.com/en/conditions/otitis-externa/) - [Community-acquired pneumonia](https://durgical.com/en/conditions/community-acquired-pneumonia/) - [Osteomyelitis](https://durgical.com/en/conditions/osteomyelitis/) - [Bronchiectasis](https://durgical.com/en/conditions/bronchiectasis/) - [Sepsis and septic shock](https://durgical.com/en/conditions/sepsis-and-septic-shock/) ## What the colours mean **Gram-positive** Thick peptidoglycan wall: stains purple. **Gram-negative** Thin wall with an outer membrane: stains pink. **Acid-fast** Lipid-rich wall (mycobacteria): Ziehl–Neelsen stain. **Contact** Gown and gloves; dedicated equipment. For C. difficile, soap-and-water hand washing. **Droplet** Surgical mask within about a metre; single room. **Airborne** N95 respirator and a negative-pressure room. [← Back to the group: Other Gram-negative rods](https://durgical.com/en/microbiology/groups/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](https://www.cdc.gov/pseudomonas-aeruginosa/about/index.html) (CDC, 2025); [Pseudomonas and Related Infections](https://www.msdmanuals.com/professional/infectious-diseases/gram-negative-bacilli/pseudomonas-and-related-infections) (MSD Manual Professional Edition, 2024); [Antimicrobial resistance](https://www.who.int/news-room/fact-sheets/detail/antimicrobial-resistance) (WHO, 2026). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/microbiology/pseudomonas-aeruginosa/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/microbiology/pseudomonas-aeruginosa/