This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Lab Investigations, Subject name: Microbiology
[{'content': "Stain for treponema - \nSelect and explain. \nA. Fontana's, B. Acid-facid, C. Methenamine-silver, D. PAS", 'role': 'user'}, {'content': 'Answer: A \nExplanation: Option 1 Microscopy: Silver impregnation method: (i) Levaditi stain (for tissue section): corkscrew shaped Treponema pallidum (ii)Fontana stain(smear)- showing the spiral morphology Option 2 Acid-fast stain is used for stain acid fast organism (Mycobacterium) or structures (Endospore). Option 3 Gomori Methenamine-Silver (GMS) stain: for fungal organisms. Option 4 Periodic Acid-Schiff (PAS) is a staining method used to detect polysaccharides such as glycogen, and mucosubstances such as glycoproteins, glycolipids and mucins in tissues.', 'role': 'assistant'}]