All of the following pathogenic bacteria fulfill Koch's postulates, except?

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