A 51-year-old woman reports a 1-year history of a chronic cough that produces a small amount of white sputum. Occasionally, the sputum is blood-streaked. 

On physical examination, her temperature is 38.0°C (100.4°F). Pulse is 71 beats/min, respiratory rate is 19 breaths/min, and blood pressure is 125/80 mmHg.

Heart sounds are faint, and there is a 15 mmHg decline in systolic arterial pressure on inspiration. 

The chest radiograph shows prominent heart borders with a “water bottle” shape. Pericardiocentesis yields 200 mL of bloody fluid. 

So, which organism is the most likely culprit? Click here to find out.