P085 The effect of gastro-oesophageal reflux on the respiratory tract microbiome

Objectives: It has been proposed that the increased amounts of gastro-oesophageal reflux seen in CF patients can lead to reflux aspiration, which in turn influences composition of the respiratory tract microbiome. The aim of this study was to assess microbial community composition and structure in the upper and lower respiratory tracts, and their relationship to intra-oesophageal measures of gastro-oesophageal reflux.Methods: CF subjects (n = 17) provided spontaneous sputum and mouth swill samples, then immediately underwent pH-impedance reflux monitoring. Genomic DNA was extracted and microbial community profiles determined by sequencing the V4 region of the 16S rRNA marker-gene using the Illumina MiSeq platform. Measures subsequently analysed included alpha-diversity (taxonomic richness, Shannon-Wiener diversity, evenness and dominance) and beta-diversity (PERMANOVA and mean distance to group centroid). Reflux measures of interest were selected (total events, proximal events and oesophageal acid exposure), and based on these the subjects were divided into tertiles for analysis.Results: Sputum samples showed no difference in alpha-diversity for any reflux measure. However, in oral rinse samples, subjects with the greatest total number of reflux events (upper tertile) had less alpha-diversity than those with the least number (lower two tertiles): richness (p = 0.016); Shannon-Wiener diversity (p = 0.007); and dominance (p = 0.007). No significant difference was noted for proximal events or oesophageal acid exposure. There were no significant differences (p > 0.05) observed in beta-diversity for any reflux measure for mouth rinses or sputum samples.Conclusions: Our data suggests that reflux does not affect the lower respiratory tract microbiome, but may influence the upper respiratory tract microbiome. This could relate to the requirement for reflux to overcome upper airway defences in order to reach the lower respiratory tract, but not the upper respiratory tract.