Increased airway iron as a potential factor in persistence of Pseudomonas aeruginosa infection in Cystic Fibrosis

¹ Cardio-Respiratory Research Group, School of Medicine, University of Tasmania, Hobart, Tasmania, Australia

^* To whom correspondence should be addressed. E-mail: d.e.c.reid{at}utas.edu.au.

	Abstract

Iron availability is critical to many bacteria and increased iron in airway secretions in cystic fibrosis (CF) has been described.

To assess the relationship between iron in CF sputum and quantitative bacterial burden.

Iron, ferritin and total cell counts (TCC) were assessed in sputum samples obtained from 15 clinically stable CF patients chronically infected with Pseudomonas aeruginosa. We also obtained sputum samples at the commencement of 10 episodes of acute exacerbation and repeated analyses in six of these exacerbations after intravenous antibiotic treatment. The relationship between iron indices and colony forming units (CFUs)·ml^-1 of P. aeruginosa as well as total anaerobic bacterial load was determined. Sputum was also obtained from 10 CF patients who had not previously isolated P. aeruginosa and 11 healthy normal controls.

Sputum iron, ferritin and TCC were significantly elevated in all CF patients, even in those not infected with P. aeruginosa, compared to healthy controls. There was a strong positive relationship between sputum iron and CFUs·ml^-1 of P. aeruginosa in clinically stable patients (R²=0.67, P<0.001), but not in samples obtained during an acute exacerbation. There was no relationship between sputum iron and anaerobic bacterial load. Antibiotic treatment significantly reduced sputum TCC and anaerobic bacterial load during an exacerbation, but not iron, ferritin or P. aeruginosa CFUs.

Increased airway iron may be important to P. aeruginosa persistence in CF.

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