A 58-year-old male with COPD and recent hospitalization presents with fever (38.9°C), productive cough with greenish sputum, and dyspnea for 3 days. Chest X-ray shows bilateral lower lobe infiltrates. Sputum culture grows a gram-negative rod that is oxidase-positive, produces a fruity odor, and grows on cetrimide agar. Blood cultures remain negative. Which of the following is the most appropriate initial empirical antibiotic regimen for this patient?