This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Bacteriology, Subject name: Microbiology
[{'content': "A man, after skinning a dead animal, developed a pustule on his hand as shown. A smear prepared from the lesion showed the presence of Gram positive bacilli in long chains which were positive for McFadyean's reaction. The most likely aetiological agent is : \nSelect and explain. \nA. Clostridium tetani, B. Listeria monocytogenes, C. Bacillus anthracis, D. Actinamyces sp", 'role': 'user'}, {'content': 'Answer: C \nExplanation: The history (animal contact), clinical picture (pustule in the area of contact) and lab findings (gram positive bacilli in chains with McFadyean reaction positive) are all characteristic of infection by Bacillus anthracis . Reference: Ananthanarayan and Paniker&;s Textbook of Microbiology Tenth edition', 'role': 'assistant'}]