Treponema pallidum (Nichols strain) in tissue cultures: cellular attachment, entry, and survival

The interaction of Treponema pallidum (Nichols strain) with cultured cells was investigated under aerobic conditions. Cell monolayers derived from rabbit testicular tissue extended the survival of treponemes as indicated by active motility. Large numbers of organisms rapidly attached to cultured cells. Within 3 h, one to twelve actively motile treponemes were attached to 25 to 50% of the cells. In addition, T. pallidum attained intracellularity as early as 30 min after inoculation of the cell monolayers. In sharp contrast, T. phagedenis biotype Reiter and T. denticola did not attach and did not enter cultured cells. Most importantly, intracellular and/or attached T. pallidum retained virulence for at least 24 h. Similar observations of attachment and retention of virulence were detected with ME-180, a cell line derived from a human cervical carcinoma. Preliminary studies with superoxide dismutase indicated that this enzyme prolonged treponemal motility and retention of virulence in the presence of cultured cells. These data provide guidelines for further investigations of in vitro cultivation of T. pallidum.