Chronic bronchial infection/colonisation: Aetiology and mechanisms

Chronic lung diseases that have prominent airway pathology accompanied by a change in themicrobial flora of the lung include cystic fibrosis (CF), non-CF associated bronchiectasis, diffuse panbronchiolitis and chronic obstructive pulmonary disease (COPD). The presence of microbial pathogens in the lower airway has been demonstrated in several different ways to have damaging effects in these diseases, and is not innocuous colonisation. Bacterial and host mechanisms contribute to the pathogenesis of this chronic infection, especially disruption in innate lung defence. Several such defects in innate lung defence have been recently described in COPD, including impairment of mucociliary clearance and macrophage function, as well as deficiencies in immunoglobulin A and antimicrobial peptides. Important bacterial persistence mechanisms include host cell invasion, biofilm formation and antigenic alteration.