This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General Microbiology Pa 1 (History, Microscopy, Stains and Structure and Physiology of Bacteria), Subject name: Microbiology
Silver impregnation technique is used in the identification of - 
Select and explain. 
A. Spirochetes, B. Leptospira, C. Borrelia, D. All of the above
D: All of the above
Answer: D: All of the above 
Explanation: Impregnation stains: - Cells and structures that are too thin to be visualized by the light microscope can be rendered visible by impregnation of silver on their surface. Silver impregnation method is a common method used for staining spirochetes, such as T. pallidum, Leptospira, Borrelia, etc. Histology = Treponema pallidum grow in Rabbit's testis. Brown color stained with Fontana Silver Impregnation stain.