Development and utilization of <i>Treponema pallidum</i> expressing green fluorescent protein to study spirochete-host interactions and antibody-mediated clearance: expanding the toolbox for syphilis research

Syphilis, a sexually transmitted infection caused by <i>Treponema pallidum</i> (<i>TPA</i>), remains a pressing threat to global public health. <i>TPA</i> has a remarkable and still poorly understood ability to disseminate rapidly from the site of inoculation and establish persistent infection throughout the body. Recent advances in <i>in vitro</i> cultivation and genetic manipulation of syphilis spirochetes enabled the development of fluorescent <i>TPA</i>. In the study, we generated and characterized an infectious <i>TPA</i> strain that constitutively expresses green fluorescent protein and used this strain to visualize the interaction of <i>TPA</i> with host cells and functionally characterize antibodies directed against treponemal outer membrane proteins. Most notably, we assessed the ability of surface-bound antibodies to inhibit the growth of <i>TPA in vitro</i> and/or disrupt the spirochete's fragile outer membrane. Fluorescent <i>TPA</i> strains provide a powerful new tool for elucidating host-pathogen interactions that enable the syphilis spirochete to establish infection and persistent long-term within its obligate human host.