Q. A 27-year-old woman with cystic fibrosis visits her pulmonologist, concerned about a worsening productive cough, increased shortness of breath, and fatigue over the past two weeks. Her vital signs are as follows: temperature 100.4°F (38°C), blood pressure 110/70 mmHg, pulse 95/min, and respiratory rate 24/min. She has a history of smoking but quit a year ago. On examination, crackles are heard in both lung fields. A sputum culture is ordered to identify the causative organism for her pneumonia. Which of the following organisms is the most likely cause of pneumonia in this adult patient with cystic fibrosis?