A 62-year-old man with chronic obstructive pulmonary disease presents with purulent sputum and fever. Sputum culture grows a Gram-negative rod that is oxidase-positive and non-fermenting. On blood agar, colonies are surrounded by a greenish discoloration of the medium. Which feature most reliably distinguishes this isolate from *Burkholderia cepacia*, another common respiratory pathogen in COPD?