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
All of the following pathogenic bacteria fulfill Koch's postulates, except? 
Select and explain. 
A. Treponema pallidum, B. Yersinia pestis, C. Bacillus anthracis, D. Helicobacter pylori
A: Treponema pallidum
Answer: A: Treponema pallidum 
Explanation: According to Koch's postulate: it must be possible to isolate a bacterium from the site of lesion and grow it in a cell-free culture medium. Pathogenic Treponemes do not grow in a cell-free aificial culture medium. Ref: Textbook of Microbiology; Ananthanarayan and Paniker; 9th edition; Pg no: 370