Successful long-term in vitro cultivation of Treponema pallidum subsp. pertenue strains of human and non-human primate origin

The long-term in vitro cultivation system for Treponema pallidum enabled in vitro propagation of several historical and contemporary T. pallidum subsp. pallidum (TPA) strains as well as T. pallidum subsp. endemicum (TEN) strain Bosnia A. In contrast, the long-term in vitro cultivation of T. pallidum subsp. pertenue (TPE) remained challenging. In this study, we demonstrate the first successful long-term in vitro cultivation of TPE strains including CDC-2, a human yaws isolate, and strain Fribourg-Blanc, a simian isolate. The in vitro cultivation of TPE Gauthier (a human yaws isolate) was positive for presence of treponemes/treponemal DNA for 24 weeks, however, the Gauthier growth rate was insufficient for long-term stable cultivation. In accordance with findings from long-term cultivation, binary co-cultivation with the TPA strain DAL-1 (generation time: 33 h) revealed generation times of 41.7 h for CDC-2 and 49.0 h for Fribourg-Blanc. Furthermore, the first descriptive proteomic characterization of TPE strains CDC-2 (776 detected proteins; 72.7% of annotated proteins) and Fribourg-Blanc (694 detected proteins; 65.2% of annotated proteins), as well as TEN strain Bosnia A (889 proteins; 83.6% of annotated proteins), have been achieved from in vitro cultures. The established in vitro cultivation of TPE provides an important tool to advance studies focused on yaws pathogenesis and non-human primate infections.