Schematic Representation of the mucociliary escalator in the non-cystic fibrosis and cystic fibrosis (CF) airways. In the non-CF airway (Fig. 2A), where the depth of the periciliary fluid is normal, islands of mucus float on top and are propelled upward toward the mouth by the coordinated beating of cilia. In the CF airway (Fig 2B), the mucus is poorly hydrated and hypoxic. Because of the decreased depth of the periciliary fluid, the abnormal mucus is plastered down upon the cilia, thus inhibiting normal ciliary beating. Eventually the bacteria present in the airway become trapped in the mucus and adapt to the local environment. In the case of P. aeruginosa, this includes production of mucoid exopolysaccharide (MEP) and organization into a biofilm.