The role of respiratory protection on increased survival of Treponema pallidum (Nichols) when cocultivated with mammalian cells in vitro.

The ability of mammalian cells in tissue culture to protect against oxygen toxicity for Treponema pallidum was examined. Addition of catalase to the incubation medium enhanced T. pallidum survival when co-incubation was carried out under aerobic conditions. When co-incubation was carried out under 3% oxygen, catalase had no enhancing effect on survival despite the fact it was still highly stimulatory when T. pallidum was incubated under 3% oxygen in the same medium with no tissue culture cells present. Inactivation of the catalase present endogenously in the mammalian cells by the addition of the catalase inhibitor 3-amino-1,2,4-triazole largely eliminated the enhancing effect of mammalian cells on the survival of T. pallidum under 3% oxygen. Increasing the oxygen consumption of the host mammalian cells with 0.1 mM 2,4-dinitrophenol enhanced T. pallidum under both aerobic and microaerobic conditions; a much greater effect was seen under aerobic conditions. The results indicated that mammalian cells offer significant protection against toxic oxygen reduction products for T. pallidum in vitro under microaerobic conditions.