Loss of Treponema pallidum during incubation in Nelson's survival medium with or without serum added.

Treponema pallidum organisms suspended in equal parts of Nelson's survival medium alone and with addition of various sera were counted in 5 microliters samples before and after 18 hours' anaerobic incubation at 35 degrees C. Samples in which the treponemes were not Poisson-distributed were excluded from the study. A loss of greater than 30% occurred in 230 out of 391 samples. The disappearance of treponemes did not seem to be caused by treponemal agglutination during incubation. There was no adherence of treponemes to the formed elements remaining in the suspension. The loss was not dependent on the concentration of syphilitic serum, nor was it influenced by the presence of immobilizing antibody in the serum. Lack of rigorous anaerobiosis during the manipulations did not influence the treponemal loss. The loss was independent of the density of the treponemal suspensions which did not contain unheated guinea-pig serum (GPS). The relative frequency of the loss exceeding 30% was highest in suspensions containing unheated GPS. However, the extent of loss in individual samples was haphazardly distributed among suspensions of all the compositions examined. The loss of treponemes seems to depend on at least two factors: a) a factor which is eluted together with the treponemes from the syphilitic orchitis and b) the presence of active guinea-pig complement. It is conjectured that the complement is non-immunologically activated and acts through the alternative pathway.