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The lipid composition of Treponema pallidum (Nichols virulent strain) was determined after purification of the organisms from the infected testes of corticosteroid-treated rabbits by differential centrifugation, filtration through Nuclepore membranes, and sedimentation in Hypaque density gradients. The total lipids were comprised of 32.2% neutral lipids, mainly cholesterol, and 67.8% phospholipids consisting of phosphatidylcholine (32.1%), sphingomyelin (14.8%), cardiolipin (13.0%), phosphatidylethanolamine (6.2%), phosphatidylinositol-serine (1.2%), and lysophosphatidylcholine (0.4%). Monoglycosyldiglyceride, a glycolipid comprising 25 to 50% of the total lipid of all Treponema previously examined, was not detected. The fatty acid composition was similar but quantitatively distinct from that of the infected testes tissue.Attempts to cultivate Treponema pallidum, the causative agent of syphilis, in vitro have failed since its discovery almost 75 years ago. Largely due to this, little is known about the organism's lipid metabolism or composition. Many cultivable Treponema require long-chain fatty acids for growth (9,16,22) since they can neither synthesize, 8-oxidize, nor desaturate fatty acids (1,10,19). Some intestinal and oral strains, however, can utilize short-chain fatty acids (26). Recent studies suggest that T. pallidum may also have lesions in lipid metabolism similar to many cultivable treponemes (9,18,21,25).Lipids comprise 15 to 20% of the cellular dry weight of the cultivable treponemes (10, 16). The major component is a glycolipid, monoglycosyldiglyceride (MGDG), containing galactose generally as the sugar moiety. MGDG comprises 25 to 50% of the total lipid of each of the approximately 20 treponemal strains of genital, oral, and intestinal origin so far examined (10,16,19) including T. hyodysenteriae (our unpublished data), the only cultivable pathogenic Treponema (12). Although Vaczi et al. (29) investigated the lipid composition of T. pallidum (Budapest strain), as well as four cultivable treponemes, they reported no quantitative data about the individual lipids or gave any indication of the glycolipid content of the organisms.Since T. pallidum cannot be cultivated in vitro, the organism is obtained for laboratory studies from the testes of experimentally infected rabbits. A major impedance of research on T. pallidum is the difficulty of obtaining large yields of the organism free of rabbit testicular material. In recent years, however, the use of corticosteroid-treated rabbits (8), Nuclepore filters (25), and Hypaque gradients (2) has proven remarkably useful in reducing this problem. We have used all of these tools to obtain high numbers of purified T. pallidum for lipid analysis. Infected rabbit testicular tissue and T. phagedenis biotype reiterii were also examined as comparative controls. Our results have shown that T. pallidum appears to be unique among Treponema in that the major lipid component of other Treponema, namely MGDG, was not detected in this human pathogen.MATERIALS AND METHODS C...

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Treponema pallidum (Nichols virulent strain) was incubated with or without oxygen, using a modified medium supplemented with reduced glutathione and a variety of nutrients (PRNFjo-B). Twoto fourfold increases in treponemal numbers were observed in cultures without mammalian cells within 96 h of incubation under 5 to 6% oxygen. Treponemal motility and multiplication were maintained more satisfactorily in cultures that were diluted and transferred daily, using an equal volume of fresh medium. Treponemes incubated without oxygen did not significantly increase in number. Virulent microorganisms were detected for at least 96 h in the cell-free system. In the presence of 3 to 4% oxygen, two-to fivefold increases in treponemal numbers were observed in the supernatant fluids of cultures containing human prepuce cells after 48 to 120 h at 35°C. Without oxygen, treponemal numbers rarely approached a threefold increase. Virulent treponemes were detected by the rabbit skin lesion test after at least 120 h in vitro. Regardless of the system of incubation, increases in treponemal numbers could not be sustained for longer than 120 h, and treponemal virulence decreased as a function of time in vitro.