Brief report. separation of pathogenic Treponema pallidum from host rabbit tissue to obtain virulent and viable microorganisms.

T. pallida extracted from infected rabbit testes were purified from different tissue particles by equilibrium density centrifugation at 25 degrees C after layering on a column of Ficoll-sodium metrizoate solution. After centrifugation, 32 per cent of the treponemes were present in a visible band and about 57 per cent were concentrated in the three ml suspension just above the interface between the Ficoll-Na metrizoate cushion and treponeme-containing medium. The treponemes were viable, virulent and retained their morphological integrity, infectivity, and antigenicity. Purity of the different fractions was studied by immunodiffusion experiments. The purified preparations of virulent, viable treponemes will provide a better antigen in the FTA-ABS tests and possibly in the TPI and TPHA tests; in cellular immunity studies, electron microscopic investigations of the ultrastructure of treponemes, vaccination studies and in tissue culture investigations.