Pseudomonas aeruginosais an aerobic Gram-negative rod; it is an opportunistic pathogen that causes disease in patients with impaired host defenses. The defenses may be generally weakened by debility or cancer, or there may be an artificial breach in the defenses, such as an endotracheal tube, or specific humoral or cellular defects, such as seen in cystic fibrosis (CF).P aeruginosais particularly associated with progressive and ultimately fatal chronic respiratory infection in CF; patients with other forms of bronchiectasis may contract chronic infection that may be impossible to eradicate despite vigorous treatment.P aeruginosais a significant cause of nosocomial pneumonia, and several risk factors have been identified. Various bacterial products contribute to the pathogenicity of the bacterium. An exuberant chronic inflammatory response causes lung damage in bronchiectasis, whereas the acute inflammatory response may be inadequate in pneumonia, which is associated with bacteremia and high mortality.P aeruginosais inherently resistant to many antibiotics at concentrations that can be achieved in vivo, and with the exception of some quinolones, the antibiotics to which it is sensitive need to be given intravenously. A semisynthetic penicillin or third-generation cephalosporin is commonly used together with an aminoglycoside. In bronchiectasis, barriers to antibiotic penetration to the site of infection may reduce efficacy, and the use of nebulized antibiotics is an approach that attempts to overcome this. Future research will concentrate on preventative strategies and adjunct therapies to improve outcome.