Pneumocystis jirovecii (Pneumocystis pneumonia)

A 41-year-old man presents to the emergency department with a worsening cough, dyspnea, and fever for the past two days. The patient is HIV positive; the last CD4 count was 180 cells /mm³. His last viral count was 150,000 copies/mL. The patient is poorly compliant with antiviral therapy. Temperature is 39.4 C° (103 F°), pulse is 90/minute, respiratory rate 25/min, blood pressure is 120/70 mmHg, and oxygen saturation is 82% on room air. Physical examination shows diffuse lung crackles on auscultation. A CT scan of the chest is shown below. Which is the most likely causative organism for this patient’s condition?
 
^{Reproduced from Radiopedia}