This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: general microbiology, Subject name: Microbiology
Organisms that have not been cultured successfully so far is? 
Select and explain. 
A. Leptospira, B. Treponema pallidum, C. Bordetella, D. Staphylococcus
B: Treponema pallidum
Answer: B: Treponema pallidum 
Explanation: Pathogenic Treponemes do not grow in aificial culture media. They require a living organism like a virus for their growth REF: Textbook of microbiology Ananthanarayan, and Paniker. Page no.: 371