Inhibition of macromolecular synthesis in cultured rabbit cells by Treponema pallidum (Nichols)

A review of in vitro attempts to develop the axenic culture of Treponema pallidum and genomics-based suggestions to achieve this elusive goal

To date, the axenic culture of Treponema pallidum remains a challenge in the field of microbiology despite countless attempts. Here, we conducted a comprehensive bibliographic analysis using several databases and search engines, namely Pubmed, Google scholar, Google, Web of Science and Scopus. Numerous unsuccessful empiric studies have been conducted and evaluated using as criteria dark-field microscopic observation of motile spiral shaped cells in the culture and virulence of the culture through rabbit infectivity. All of these studies failed to induce rabbit infectivity, even when deemed positive after microscopic observation leading to the misnomer of avirulent T. pallidum. In fact, this criterion was improperly chosen because not all spiral shaped cells are T. pallidum. However, these studies led to the formulation of culture media particularly favourable to the growth of several species of Treponema, including Oral Microbiology and Immunology, Zürich medium (OMIZ), Oral Treponeme Enrichment Broth (OTEB) and T-Raoult, thus allowing the increase in the number of cultivable strains of Treponema. The predicted metabolic capacities of T. pallidum show limited metabolism, also exhibited by other non-cultured and pathogenic Treponema species, in contrast to cultured Treponema species. The advent of next generation sequencing represents a turning point in this field, as the knowledge inferred from the genome can finally lead to the axenic culture of T. pallidum.

Syphilis: review with emphasis on clinical, epidemiologic, and some biologic features

Syphilis is a chronic disease with a waxing and waning course, the manifestations of which have been described for centuries. It occurs worldwide, and the incidence varies significantly with geographic location. Transmission is mainly by sexual contact. The causative organism, Treponema pallidum, was first described in 1905, but because of the inability to culture the organism and the limitations of direct microscopy, serologic testing is the mainstay of laboratory diagnosis. The disease has been arbitrarily divided into several stages. The primary stage is defined by a chancre at the site of inoculation. The secondary stage is characterized by a polymorphic rash, lymphadenopathy, and other systemic manifestations. A variable asymptomatic latent period follows, which for epidemiologic purposes is divided into early (<1 year) and late (>1 year) stages. The early stages (primary, secondary, and early latent) are potentially infectious. The tertiary stage is the most destructive and is marked by cardiovascular and neurologic sequelae and gummatous involvement of any organ system. Congenital infection may result in protean early or late manifestations. Unlike many other bacteria causing infectious diseases, the organism remains sensitive to penicillin, and this remains the mainstay of therapy.

Complete genome sequence of Treponema pallidum, the syphilis spirochete

The complete genome sequence of Treponema pallidum was determined and shown to be 1,138,006 base pairs containing 1041 predicted coding sequences (open reading frames). Systems for DNA replication, transcription, translation, and repair are intact, but catabolic and biosynthetic activities are minimized. The number of identifiable transporters is small, and no phosphoenolpyruvate:phosphotransferase carbohydrate transporters were found. Potential virulence factors include a family of 12 potential membrane proteins and several putative hemolysins. Comparison of the T. pallidum genome sequence with that of another pathogenic spirochete, Borrelia burgdorferi, the agent of Lyme disease, identified unique and common genes and substantiates the considerable diversity observed among pathogenic spirochetes.

Experimental syphilitic orchitis. Relationship between Treponema pallidum infection and testis synthesis of proteoglycans

The relationship between Treponema pallidum infection and the synthesis of proteoglycans by organ cultures of rabbit testes was investigated. Two proteoglycan fractions, large (CL-6B Kav 0.05) and small (Kav 0.25), that were not synthesized at detectable levels by cultures from rabbits infected with T. pallidum for 0 or 5 days, were produced by cultures from 10-, 15- and 20-day infected rabbits. The small proteoglycan appeared to be synthesized first because greater amounts of this fraction were detected in extracts of cultures from 10-day infected animals. The large proteoglycan fraction may have been induced directly by T. pallidum because increased synthesis correlated with maximal treponemal numbers, 15 days after infection. In contrast, the induction of the smaller proteoglycan did not appear to be directly related to numbers of elutable organisms. The proteoglycans synthesized between 10 and 20 days after infection were analyzed for glycosaminoglycan (GAG) size and composition. The size of GAGs beta-eliminated from the proteoglycans generally increased over the 10-20-day infection period. Whereas the composition of the small proteoglycan fraction was largely unchanged during the 10-20-day period (45% chondroitin sulphate (CS), 55% dermatan sulphate (DS)), the amount of DS in the high molecular weight proteoglycan fraction decreased from 50-20% during this period (CS 50-80%). Autoradiography studies revealed that increased proteoglycan synthesis in T. pallidum-infected testes was localized to cells lining the seminiferous tubules and to fibroblasts infiltrating peritubular spaces.

Inhibitory effect of syphilitic rabbit serum on DNA synthesis in rabbit cells in vitro

A previously described toxic factor associated with Treponema pallidum (Nichols) and found in extracts of syphilitic rabbit testes has now also been detected in syphilitic rabbit serum. The toxic factor, which inhibits DNA synthesis in baby rabbit genital organ (BRGO) cells in vitro, is present in rabbit serum up to 30 days after infection with T pallidum.

Polyanions in syphilis: evidence that glycoproteins and macromolecules resembling glycosaminoglycans are synthesised by host tissues in response to infection with Treponema pallidum

We investigated by means of radiolabelled precursors the source and nature of the polyanionic macromolecules present in rabbit tissues during active syphilis infection. Previous studies indicated that Treponema pallidum itself does not synthesise glycosaminoglycans, at least in vitro. In replicate experiments on unilaterally infected rabbits, tissue from the orchitic testis incorporated two to three times more 35S-sulphate and 3H-glucosamine (on a wet weight basis) than tissue from the non-orchitic contralateral testis. Incorporation of 35S-sulphate was independent of the number of viable T pallidum organisms present in the infested tissue, which suggested that incorporation represented biosynthesis by the host and not the treponeme. Testes from syphilitic rabbits two days after treatment with high doses (100 mg/kg) of penicillin incorporated less 35S-sulphate than untreated infected testes, but more than normal uninfected rabbit testes. This suggests that active syphilitic infection was necessary for maximum biosynthesis of the macromolecule(s) by host tissue. Hydrodynamic profiles showed incorporation of radiolabelled precursors into two distinct fractions of different sizes, which may represent a proteoglycan and a sulphated glycoprotein. Alcian blue staining of syphilitic testes at or after peak orchitis showed focal deposition of newly synthesised polyanionic components during peak orchitis and a more generalised fibrosis in testes after peak orchitis.

Treponema pallidum does not synthesise in vitro a capsule containing glycosaminoglycans or proteoglycans

Treponema pallidum was investigated for its ability to synthesise glycosaminoglycans or proteoglycans in vitro. Isolated viable T pallidum organisms were incubated with radiolabelled precursors of glycosaminoglycans, sodium 35S-sulphate and 3H-glucosamine (tritiated glucosamine). T pallidum failed to incorporate sodium 35S-sulphate but did incorporate 3H-glucosamine into a macromolecule which may be associated with the surface of the treponeme. This macromolecule was resistant to degradation by specific glycosaminoglycanases. We conclude that T pallidum does not synthesise a capsule containing glycosaminoglycans in vitro.