 This study will evaluate the effects of budesonide using Symbicort which is budesonide and formoterol and fluticasone using Advair which is fluticasone and salmeterol on the airway microorganisms of patients with moderate-to-severe chronic obstructive pulmonary disease COPD. This is a randomized, parallel group, two-centered clinical trial study to evaluate the effects of a 12 week treatment with Symbicort 400 mcg BID and Advair 250 mcg BID via Diskus on airway microbiota in patients with moderate-to-severe COPD. The control arm of this study will be Oxeze 12 ug BID. 