You are answering a USMLE-style medical question. Question: A 68-year-old man presents to the emergency department because of fever, abdominal pain, and rapidly progressive distension of the abdomen. His appendix was removed for an abscess 3 days ago. The complete blood count showed leukocytosis. Anaerobic culture of the peritoneal fluid needle aspirate showed a gram-negative pathogen. Which of the following, in addition to polymicrobial infection, is the most likely cause of this patient’s condition? Options: A) Bacteroides fragilis B) Campylobacter jejuni C) Clostridium perfringens D) Shigella sonnei Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.