This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Microbiology
[{'content': 'A patient admitted to an ICU is on central venous line for the last one week. He is on Ceftazidime and amikacin. After 7 days of antibiotics he develops a spike of fever and his blood culture is positive for gram positive cocci in chains which are catalase - negative. Following this vancomycin was started but the culture remained positive for same organism even after 2 weeks of therapy. The most likely organism causing infection is : \nSelect and explain. \nA. Staphylococci aureus, B. Viridans streptococci, C. Enterococcus faecalis, D. Coagulase negative staphylococcus', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]