The link between dysfunction of the CFTR protein and the pathophysiology of lung disease in cystic fibrosis (CF) has recently become clearer. Abnormal sodium and chloride ion transport in respiratory epithelial cells results in depletion of airways surface liquid volume, delayed mucus transport, and impaired bacterial clearance.^1,2 This initiates airways inflammatory responses leading, ultimately, to lung injury in CF. The most important predictors of poor outcome are chronic infection with Pseudomonasaeruginosa and Burkholderiacepacia complex and reduced forced expiratory volume in 1 second (FEV₁).^3–5

Pseudomonasaeruginosa

Pulmonary infection in CF is characterised by a narrow spectrum of micro-organisms and is dominated in older patients by Paeruginosa. This organism and other related Gram-negative bacteria adapt to the conditions found in airways mucus and establish biofilms which allow chronic infection to be established.⁶ Recent studies suggest that this microenvironment is relatively hypoxic and this creates a hospitable environment for P aeruginosa which, when exposed to low oxygen concentrations, increases alginate formation which assists in the development of micro-colonies within a biofilm.⁷ The biofilm protects Paeruginosa from host defence, bacterial clearance mechanisms, and antibiotics. In addition, bacterial adherence to mucus is increased in CF which may also contribute to difficulties in clearing it from the airways.⁷

The source of early Paeruginosa infection is either the environment or other patients with CF. Aggressive treatment of early infection with this organism can frequently eliminate it for some years but, by the end of the second decade, over 80% of patients with CF have chronic Pseudomonasaeruginosa infection.^8,9

Recent studies have shown that, in some CF centres, clonal spread of Paeruginosa …