Dennis W. Nielson

Bacterial communities in the airways of cystic fibrosis (CF) patients are, as in other ecological niches, influenced by autogenic and allogenic factors. However, our understanding of microbial colonization in younger versus older CF airways and the association with pulmonary function is rudimentary at best. Using a phylogenetic microarray, we examine the airway microbiota in age stratified CF patients ranging from neonates (9 months) to adults (72 years). From a cohort of clinically stable patients, we demonstrate that older CF patients who exhibit poorer pulmonary function possess more uneven, phylogenetically-clustered airway communities, compared to younger patients. Using longitudinal samples collected form a subset of these patients a pattern of initial bacterial community diversification was observed in younger patients compared with a progressive loss of diversity over time in older patients. We describe in detail the distinct bacterial community profiles associated with young and old CF patients with a particular focus on the differences between respective "early" and "late" colonizing organisms. Finally we assess the influence of Cystic Fibrosis Transmembrane Regulator (CFTR) mutation on bacterial abundance and identify genotype-specific communities involving members of the Pseudomonadaceae, Xanthomonadaceae, Moraxellaceae and Enterobacteriaceae amongst others. Data presented here provides insights into the CF airway microbiota, including initial diversification events in younger patients and establishment of specialized communities of pathogens associated with poor pulmonary function in older patient populations.

Prior studies have shown that fluid secretions from airway submucosal glands in cystic fibrosis (CF) are reduced and hyperviscous, possibly contributing to the pathogenesis of CF airway disease. Because the CF transmembrane conductance regulator (CFTR) protein can transport both chloride and bicarbonate, we investigated whether gland fluid pH is abnormal in early CF, using nasal biopsies from pediatric subjects having minimal CF lung disease. Gland fluid pH, measured in freshly secreted droplets under oil stained with BCECF-dextran, was 6.57 +/- 0.09 (mean +/- SE) in biopsies from six CF subjects, significantly lower than 7.18 +/- 0.06 in eight non-CF biopsies (P < 0.01). To rule out the possibility that the apparent gland fluid hyperacidity in CF results from modification of fluid pH by the airway surface, a microcannulation method was used to measure pH in fluid exiting gland orifices. In pig trachea and human bronchi, gland fluid pH was reduced by up to 0.45 units by CFTR inhibitors, but was not affected by amiloride. Acid base transport in the surface epithelium of pig trachea was studied from pH changes in 300-nl fluid droplets deposited onto the oil-covered airway surface. The droplets had specified ionic composition/pH and/or contained transporter activators/inhibitors. We found evidence for CFTR-dependent bicarbonate transport by the tracheal surface epithelium as well as ATP/histamine-stimulated proton secretion, but not for sodium/proton or chloride/bicarbonate exchange. These results provide evidence for intrinsic hyperacidity in CF gland fluid secretions, which may contribute to CF airway pathology.

We measured the pH of the alveolar subphase fluid by puncturing the most superficial alveoli of the exposed lungs of anesthetized rabbits with H+-selective and nonselective KCl microelectrodes. In these experiments, we bathed the lung surface with paraffin oil or buffered Ringer's solutions that had a CO2 tension of 40 Torr (1 Torr = 133.3 Pa) and found an alveolar pH of 6.92 +/- 0.01 (mean +/- sEM). When the pH of the surface buffer was below 6.7 or above 7.5, alveolar pH varied with surface buffer pH. With the nonselective electrode, we did not find a significant electrical potential difference between the alveolar fluid and the pleural surface. These results are consistent with active transport of H+ (or HCO3(-) across alveolar epithelium.