 Pseudomonas aeruginosa PA is associated with chronic lung infections in patients with chronic obstructive pulmonary disease COPD. Commensal flora microbiota in lung was recently described using high-throughput sequencing techniques NGS. PA strains isolated during lung infection episodes of severe COPD patients often show resistance to antibiotics including imipenem that is mainly due to mutation in oprD. In collaboration with Harvard Medical School, the investigators have recently demonstrated that PA OprD mutant shows increased survival fitness and its virulence. This bacterium could be more likely to colonize. Colonization by PA OprD mutant could influence the pulmonary microbiota and may worsen disease evolution, particularly in terms of frequency of exacerbations. Our objective is to describe modification of pulmonary microbiota associated with PA colonization, including OprD PA mutant, in severe COPD patients. The investigators will correlate the microbiota modification to medical history. Stable severe COPD patients will be included. Three groups of patients will be sampled: 1 not PA colonized, 2 PA colonized and 3 PA OprD mutant colonized. Medical history will be recorded by the physician as usual and three samples will be performed: 1 sputum, 2 oral wash and 3 water used for oral wash. Regular bacterial culture will be performed and NGS will be performed also to characterize the microbiota. 