 Patients: Severe COPD Patients FEVForced vital capacity FVC70 and in FEV50 after bronchodilation hospitalized in the pulmonology Department of the Reims Teaching Hospital. At the inclusion, patients should be stable. Inclusion of 20 patients needing 100 patients in total will require 24 months.The study of associated factors with colonization to PA and PA mutant OprD will be performed only for patients known to be not PA carrier. Microbiota characterization will be performed on all patients colonized with PA and on non PA colonized patients randomly selected. The analysis of of PA colonization influence on COPD evolution will be done 12 months after sampling for all patients included. 