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 microbiologist carries out milk ring test, which is positive. What is the most likely organism? \nSelect and explain. \nA. Salmonella, B. Brucella, C. Bordetella, D. Bacillus anthracis', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Milk Ring Test (M) is positive for Brucella. It is used for detection of infected animals in dairy farms, etc. A sample of whole milk is mixed with a drop of Brucella antigen and incubated at 70 degC for 40-50 min. If antibodies are present in the milk the bacilli are agglutinated and rise with the cream to form a blue ring at the top, leaving the milk unstained (M positive). If antibodies are absent, the milk remains uniformly blue (M negative) Reference: Ananthanarayan and Paniker&;s Textbook of Microbiology Tenth edition', 'role': 'assistant'}]