Because of their embryological derivation from foregut the respiratory airways are regularly host to bacteria arriving in inspired air and aspirated from the naso-oropharynx. Should the first-line defence (mucociliary clearance) be less than perfect, such bacteria remain longer in the airway mucus and some are able to capitalize on this delay by compromising mucus transport further through the production of epithelium-damaging cilioinhibitory and ciliotoxic substances. Bacterial persistence in the airways elicits an inflammatory host response which causes further damage to the airway and results in a 'vicious circle' of progressive lung damage. Treatment hinges upon eliminating the bacteria in the mucus using antibiotics that penetrate mucus well (e.g. fluoroquinolones)--and considering adjunct therapy with anti-inflammatory and mucokinetic agents.