Pseudomonas aeruginosa is a Gram‑negative, rod‑shaped bacterium with a single polar flagellum. It belongs to the Gammaproteobacteria and is non‑fermentative, deriving energy from aerobic respiration. The bacterium produces distinctive pigments including pyocyanin (blue‑green) and pyoverdine (yellow‑green), giving cultures a characteristic color and odor. P. aeruginosa thrives in soil, water and on surfaces with minimal nutrients due to its metabolic versatility and robust stress responses. Its outer membrane has low permeability and it expresses multiple efflux pumps, contributing to intrinsic resistance to many antibiotics and disinfectants. The bacterium readily forms biofilms on biotic and abiotic surfaces; these biofilms further enhance tolerance to antimicrobials and host defenses. Genetic plasticity and acquisition of resistance determinants, such as β‑lactamases and aminoglycoside‑modifying enzymes, make P. aeruginosa a major nosocomial threat.
Clinical significance and examples
P. aeruginosa is an opportunistic pathogen that causes severe infections in individuals with compromised defenses. In hospitals it colonizes ventilators, catheters and burn wounds, leading to ventilator‑associated pneumonia, catheter‑associated urinary tract infection and sepsis. In people with cystic fibrosis, chronic colonization of the lungs by mucoid strains leads to persistent inflammation and progressive respiratory failure. Burn patients, neutropenic individuals and those with chronic otitis externa are also at risk. Virulence factors include exotoxin A, elastases, phospholipases, rhamnolipids and quorum sensing systems that coordinate gene expression in biofilms. The bacterium’s resistance limits therapeutic options; treatment often requires combination therapy with antipseudomonal β‑lactams (such as piperacillin‑tazobactam or ceftazidime), carbapenems, fluoroquinolones or aminoglycosides. Beyond clinical settings, P. aeruginosa participates in bioremediation of hydrocarbons and contributes to nutrient cycling in soil and aquatic environments.
Pseudomonas aeruginosa illustrates how metabolic versatility and adaptive resistance can allow a ubiquitous environmental bacterium to become a formidable opportunistic pathogen. Vigilant infection control and stewardship of effective antibiotics are essential to limit its impact in healthcare settings.
Related Terms: Gram-negative bacterium, Biofilm, Opportunistic pathogen, Cystic fibrosis, Pyocyanin