Static mucus impairs bacterial clearance and allows chronic infection with<i>Pseudomonas aeruginosa</i>in the cystic fibrosis rat

Abstract

Cystic fibrosis airway disease is characterised by chronic <i>Pseudomonas aeruginosa</i> infection. Successful eradication strategies have been hampered by a poor understanding of the mechanisms underlying conversion to chronicity. The cystic fibrosis transmembrane conductance receptor (CFTR)-knockout (KO) rat harbours a progressive defect in mucociliary transport and viscosity. KO rats were infected before and after the appearance of the mucus defect, using a clinical mucoid-isolate of <i>P. aeruginosa</i> embedded in agarose beads. Young KO rats that were exposed to bacteria before the development of mucociliary transport defects resolved the infection and subsequent tissue damage. However, older KO rats that were infected in the presence of hyperviscous and static mucus were unable to eradicate bacteria, but instead had bacterial persistence through 28 days post-infection that was accompanied by airway mucus occlusion and lingering inflammation. Normal rats responded to infection with increased mucociliary transport to supernormal rates, which reduced the severity of a second bacterial exposure. We conclude that the aberrant mucus present in the CF airway permits persistence of <i>P. aeruginosa</i> in the lung.