Definition:

Pseudomonas aeruginosa is an opportunistic pathogen that may cause severe invasive diseases in critically ill patients. In the 21st century, when the life expectancy of highly susceptible immunocompromised groups has been extended in most countries, P. aeruginosa plays an increasingly prominent role in hospital infections. This organism shows a remarkable capacity to resist antibiotics, either intrinsically (because of constitutive expression of beta-lactamases and efflux pumps, combined with low permeability of the outer-membrane) or following acquisition of resistance genes (e.g., genes for beta-lactamases, or enzymes inactivating aminoglycosides or modifying their target), over-expression of efflux pumps, decreased expression of porins, or mutations in quinolone targets. These mechanisms mediate the multidrug-resistant (MDR) phenotype in P. aeruginosa.