The intestinal microbiota plays an important role in health and disease of humans. Cystic fibrosis patients suffer from lung infections that require multiple antimicrobial therapies. In addition, their intestinal physiology and food digestion are severely disturbed. The present project will use metaproteomics analyses to study the composition, dynamics and other characteristics of the distal microbiota of a cohort of cystic fibrosis patients and of their healthy siblings.