Treponema is most difficult to isolate from?

Gumma REF: Jawetz, Melnick, & Adelberg's Medical Microbiology, 24T" edition Chapter 25 "Gumma is a lesion of teiary syphilis, and treponemes are rare in teiary lesions" In about 30% of cases, early syphilitic infection progresses spontaneously to complete cure without treatment. In another 30%, the untreated infection remains latent (principally evident by positive serologic tests). In the remainder, the disease progresses to the "teiary stage," characterized by the development of granulomatous lesions (Gumma) in skin, bones, and liver; degenerative changes in the central nervous system (meningovascular syphilis, paresis, tabes); or cardiovascular lesions (aoitis, aoic aneurysm, aoic valve insufficiency). In all teiary lesions, treponemes are very rare, and the exaggerated tissue response must be attributed to hypersensitivity to the organisms. However, treponemes can occasionally be found in the eye or central nervous system in late syphilis.