Interaction of Treponema pallidum (Nichols strain) with cultured mammalian cells: effects of oxygen, reducing agents, serum supplements, and different cell types

Abstract

Cultured mammalian cells extend the time of survival of Treponema pallidum (Nichols strain). Various parameters that have been previously shown to enhance treponemal survival in vitro were examined for influences on the interaction of T. pallidum with cultured cells. With cells derived from normal rabbit testes, the time of retention of treponemal virulence was extended in an atmosphere containing reduced concentrations of oxygen. Glutathione and cysteine, when added to the basal tissue culture medium, prolonged treponemal survival. In an assessment of various tissue culture medium supplements, normal rabbit serum was equivalent to fetal bovine serum and superior to bovine serum albumin fraction V (BSA), fatty acid-poor BSA, and lipid-poor BSA. Beneficial effects on the retention of treponemal virulence were also observed for TRK-2, HSE, NRK, and C6 cells. Dithiothreitol, as an additional reducing agent, sharply enhanced treponemal survival. With SF1Ep NBL-11 cells and basal tissue culture medium containing glutathione, cysteine, and dithiothreitol, in an atmosphere of approximately 3% oxygen, T. pallidum was maintained without detectable decreases in the number of virulent organisms for 6 days.