A 26-year-old man presents with a 2-week history of fever and a cough. He was diagnosed with HIV four months ago and is not on any antiretroviral medications. His vital signs are BP 122/76, HR 78, RR 16, oxygen saturation 92% on room air, and temperature 99.2°F. Chest X-ray is shown above. Which of the following antibiotics should be used to treat this patient?