This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Systemic Bacteriology (Haemophilus, Yersinia, Spirochaetes, Ricketssia, Chlamydia, Mycoplasma and Miscellaneous Bacteria), Subject name: Microbiology
[{'content': 'In a syphilis patient, site which does not help in isolation of organism:- \nSelect and explain. \nA. Gumma, B. Primary chancre, C. Mucosal patch, D. Maculopapular rash', 'role': 'user'}, {'content': 'Answer: A \nExplanation: T. pallidum is very difficult to demonstrate in Gumma (Teiary syphilis). Infectivity of a patient to the sexual paner is maximum during primary, secondary and early latent stage. During these stages spirochetes are abundant in the lesions.', 'role': 'assistant'}]