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': "Dark ground microscopy is used for - \nSelect and explain. \nA. TPI, B. FTA - ABS, C. Kahn's test, D. VDRL", 'role': 'user'}, {'content': 'Answer: A \nExplanation: In TPI test, the serum of patient is incubated with complement and T. pallidum maintained in a complex medium anaerobically. If the antibodies are present, the treponemes are immobilized, that is, rendered nonmotile, when examined under dark ground illumination.', 'role': 'assistant'}]