Airway infection in cystic fibrosis

Early cystic fibrosis (CF) lung disease is characterised by repeated episodes of endobronchial infection and inflammation. Bronchoalveolar lavage (BAL) studies have shown that lungs of patients with CF can become infected early in infancy.

Bacteria exhibit a biofilm mode of growth in the lungs of patients with CF, with large numbers of organisms surrounded by a layer of ‘slime’ consisting of complex proteins and polysaccharides. Established biofilms are resistant to antibiotic penetration; treatment aims to eradicate bacteria before formation of the biofilm.

Lung damage is caused by an influx of circulating blood neutrophils into the airway and release of neutrophil products, including elastolytic enzymes. Neutrophil-derived DNA is also released, increasing sputum viscosity and worsening airway obstruction.

The most common organisms found in airways of patients with CF are Staphylococcus aureus, Haemophilus influenzae, Pseudomonas aeruginosa and Aspergillus species.

S. aureus and H. influenzae are the most common organisms found in infants and young children with CF. P. aeruginosa becomes the dominant organism cultured from sputum during adolescence and adulthood; see Antibiotic therapy for P. aeruginosa infection for more information.

Other organisms that may be found in airways of patients with CF include Burkholderia cepacia complex, nontuberculous mycobacterium (eg Mycobacterium abscessus), methicillin-resistant S. aureus (MRSA), other Gram-negative organisms such as Stenotrophomonas maltophilia, Achromobacter xylosoxidans and fungi.

Patterns and trends in the epidemiology of lung bacteria have changed over the past decade; see the Australian Cystic Fibrosis Data Registry annual reports (available through the Cystic Fibrosis Australia website) for more information.