This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Microbiology
All 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: Ans. is 'a' i.e., Treponema pallidum