Redox potential and survival of virulent Treponema pallidum under microaerophilic conditions.

A strongly reduced culture medium, capable of maintaining the virulence of Treponema pallidum (Nichols) for several days, was exposed to an atmosphere of 3% oxygen in nitrogen for 2-3 days before inoculation with T pallidum. By using various volumes of medium in uniform tubes a range of redox potentials (Ecal) from -94 mV to -325 mV was produced depending on the surface area-to-volume ratios of the medium. The anaerobic medium had an Ecal value of -387 mV. The medium was inoculated with T pallidum and incubated in an atmosphere of 3% oxygen. The survival of treponemes at different redox potentials was monitored by observing the retention of motility and by measuring the latent period of infection after inoculation of the cultures into the shaved backs of rabbits. Under these conditions T pallidum survived longest at low (electronegative) redox potential. An inverse linear relationship was observed between the redox potential of the culture medium and the survival of T pallidum, as measured by the time required for a 90% reduction of virulent organisms. No optimum redox potential was detected, the most electronegative medium (-325 mV, Ecal) giving the best survival.