You are answering a USMLE-style medical question. Question: A 59-year-old man comes to the emergency department because of excruciating left knee pain for 4 days. He underwent a total knee arthroplasty of his left knee joint 4 months ago. He has hypertension and osteoarthritis. Current medications include glucosamine, amlodipine, and meloxicam. His temperature is 38.1°C (100.6°F), pulse is 97/min, and blood pressure is 118/71 mm Hg. Examination shows a tender, swollen left knee joint; range of motion is limited by pain. Analysis of the synovial fluid confirms septic arthritis, and the prosthesis is removed. Which of the following is the most likely causal organism? Options: A) Staphylococcus epidermidis B) Escherichia coli C) Staphylococcus aureus D) Pseudomonas aeruginosa Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.