The basic defect in cystic fibrosis (CF) predisposes to chronic bacterial airway infections, particularly with Pseudomonas aeruginosa. Airway infections with P. aeruginosa in individuals with CF are unique in that they chronically affect a host who is immunocompetent in terms of cellular and humoral responses but is immunocompromised by impaired airway clearance. The initially acquired P. aeruginosa clone typically persists for many years in the patients' airways and thereby diversifies by de novo point mutations and the composition of its accessory genome. Co-colonizations with 2 or more clones are preferentially observed during the first 3 years of colonization. Upper and lower airways are commonly colonized by the same clone suggesting that the sinuses are the reservoir and gateway for the colonization of the lower airways. Early antipseudomonal chemotherapy has an 80% chance to eradicate the P. aeruginosa clone. This regimen introduced in the late 1980s has shifted the median age of the onset of chronic airways colonization with P. aeruginosa from school age to early adulthood at the most successful CF centres. The measures to prevent and to treat the Pseudomonas infections in CF have been considerably improved during the last 20 years. Highly transmissible epidemic strains, however, that emerge within a clonal lineage remain a major, still unresolved health threat for the CF community.
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