Persistent infections and immunity in cystic fibrosis

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Cystic fibrosis (CF) is the most common autosomal recessive lethal disease in the Caucasian population. Chronic respiratory infections with Pseudomonas aeruginosa, neutrophil-dominated airway inflammation and progressive lung damage are the major causes of morbidity and mortality in CF. Two persistent infection phenotypes expressed by this bacterium are biofilm and mucoidy. Biofilm, also called the microcolony mode of growth is the surface-associated adherent bacterial community, while mucoidy refers to a phenotype conducive to copious amounts of mucoid exopolysaccharide (MEP)/alginate that provides a matrix for mature biofilms conferring resistance to host defenses and antibiotics. Recent completion of the whole genomic sequence of the standard reference strain P. aeruginosa PAO1 has led to discoveries that many clinical isolates of this species possess unique genomic sequences (genomic islands) due to horizontal gene transfer. We propose this type of genetic exchange may play an important role in causing intrinsic genomic diversity of this organism. Therefore, the diversity, as revealed through profiles of restriction fragment length polymorphism (RFLP), may be linked to an array of novel and unexplored pathogenic mechanisms in P. aeruginosa. CF mouse models, while displaying many clinical similarities to human CF, have yet to demonstrate a chronic pulmonary disease phenotype. This review is intended to provide an overview of P. aeruginosa persistent infection phenotypes (biofilm and mucoidy) and an aerosol infection mouse model for CF. Genomic diversity of P. aeruginosa and its implications in the pathogenesis in CF will also be discussed.