Question category: Bacteriology
A 70-year-old woman is brought to the emergency department by her spouse with complaints of shortness of breath and fever. Physical examination revealed a fever of 103°F, hypotension, and a diastolic murmur. History revealed a cardiac valve replacement 5 years earlier. Three consecutive blood cultures taken during febrile periods revealed gram-positive cocci that were catalase-positive and coagulase-negative. Which of the following organisms is the most likely cause?