Treponema pallidum, formerly known as Spirochaeta pallida, is a microaerophilic, gram-negative, spirochaete bacterium with subspecies that cause the diseases syphilis, bejel (also known as endemic syphilis), and yaws. It is known to be transmitted only among humans and baboons. T. pallidum can enter the host through mucosal membranes or open lesions in the skin and is primarily spread through sexual contact. It is a helically coiled microorganism usually 6–15 μm long and 0.1–0.2 μm wide. T. pallidum's lack of both a tricarboxylic acid cycle and processes for oxidative phosphorylation results in minimal metabolic activity. As a chemoorganoheterotroph, Treponema pallidum is an obligate parasite that acquires its glucose carbon source from its host. Glucose can be used not only as a primary carbon source but also in glycolytic mechanisms to generate ATP needed to power the bacterium given its minimal genome. The treponemes have cytoplasmic and outer membranes. Using light microscopy, treponemes are visible only by using dark-field illumination. T. pallidum consists of three subspecies, T. p. pallidum, T. p. endemicum, and T. p. pertenue, each of which has a distinct related disorder. The ability of T. pallidum to avoid host immune defenses has allowed for stealth pathogenicity. The unique outer membrane structure and minimal expression of surface proteins of T. pallidum has made vaccine development difficult. Treponema pallidum can be treated with high efficacy by antibiotics that inhibit bacterial cell wall synthesis such as the beta-lactam antimicrobial penicillin-G.
Subspecies Three subspecies of T. pallidum are known:
Treponema pallidum pallidum, which causes syphilis T. p. endemicum, which causes bejel or endemic syphilis T. p. pertenue, which causes yaws The three subspecies causing yaws, bejel, and syphilis are morphologically and serologically indistinguishable. The genomes of three of the T. p. pertenue strains are similar to those of the T. p. pallidum strain, differing by only 0.2%, corresponding to virulence factors. The three subspecies can be distinguished by genetics, using restriction fragment length polymorphism (RFLP), which utilizes techniques such as PCR, restriction digest and gel electrophoresis. Genes tprC, tprI, and the 5' flanking region of tpp15 can be used to differentiate between the three subspecies based on DNA fragment lengths and location of bands in gel electrophoresis. These bacteria were originally classified as members of separate species, but DNA hybridization analysis indicates they are members of the same species. Treponema carateum, the cause of pinta, remains a separate species because no isolate is available for DNA analysis. Disease transmittance in subspecies T. p. endemicum and T. p. pertenue is considered non-venereal. T. p. pallidum is the most invasive pathogenic subspecies, while T. carateum is the least invasive of the species. T. p. endemicum and T. p. pertenue are intermediately invasive.
Laboratory identification
Treponema pallidum was first microscopically identified in syphilitic chancres by Fritz Schaudinn and Erich Hoffmann at the Charité in Berlin in 1905. Historically, this bacterium was identified in the clinical laboratory through visualization in dark field microscopy. This bacterium can be detected with special stains, such as the Dieterle stain. T. pallidum is also detected by serology, including nontreponemal VDRL, rapid plasma reagin, treponemal antibody tests (FTA-ABS), T. pallidum immobilization reaction, and syphilis TPHA test.
Microbiology
Physiology
Treponema pallidum is a helically shaped bacterium with high motility consisting of an outer membrane, peptidoglycan layer, inner membrane, protoplasmic cylinder, and periplasmic space. It is often described as gram-negative, but its outer membrane lacks lipopolysaccharide, which is found in the outer membrane of other gram-negative bacteria. It has an endoflagellum (periplasmic flagellum) consisting of four main polypeptides, a core structure, and a sheath. The flagellum is located within the periplasmic space and wraps around the protoplasmic cylinder. The flagellum is arranged in a helical shape. The flagellar motor for T. pallidum lacks a P-ring, normally used for motility, and has a collar component instead, which is imbedded in the periplasm. The peptidoglycan layer interacts with the endoflagellum which may aid in motility. T. pallidum's outer membrane has the most contact with host cells and contains few transmembrane proteins, limiting antigenicity, while its cytoplasmic membrane is covered in lipoproteins. The outer membrane adhesins of T. pallidum, including fibronectin- and laminin-binding proteins, have the main function of attaching to host cells and cell-surface receptors, and they share antigenically related functional domains. The genus Treponema has ribbons of cytoskeletal cytoplasmic filaments that run the length of the cell just underneath the cytoplasmic membrane.
Outer membrane and surface antigens The of T. pallidum has several features that have made it historically difficult to research. These include details such as its fragility. The treponemal outer membrane (OM) proteins are key factors for the bacterium's pathogenesis, persistence, and immune evasion strategies. Treponema's reputation as a "stealth pathogen" is primarily due to this unique (OM) structure, which serves to evade immune detection. The outer membrane of Treponema pallidum contains a strikingly low concentration of transmembrane proteins, approximately 100-fold lower than other gram-negative bacteria or other spirochetes. This protects the cells from antibodies attacking it, hence they exhibit a "puzzling lack of antigenicity". The genome also revealed a bundle of 12 proteins and some putative hemolysins are potential virulence factors of T. pallidum. One protein, TprK, appears to constantly mutate to avoid immune response from its host.
TP0126 The TP0126 protein has been linked to the outer membrane protein family (OMP). This protein will sit in the outer membrane like a porin, which is supported by circular dichroism recombinant TP0126, and will increase the virulence factor. Researchers have classified the TP0126 protein in this class due to the homology between the protein and the porins of the OMPs. This protein is encoded by the TP0126 gene, which is conserved over all strains of T. pallidum.
… excerpt ends here. Continue reading the full article.
