Role of serum in survival of Treponema pallidum in tissue culture.

During attempts to cultivate Treponema pallidum, it was determined that length of time for survival of virulent treponemes was highly dependent on the quality of the fetal bovine serum (FBS) used as a protein supplement in the culture medium. Eighteen lots of commercial FBS were tested for their ability to maintain survival of T. pallidum in cultures of cottontail rabbit epithelial (SflEp) cells. All were capable of supporting growth of these cells. However, in tests on five of the lots, attachment of treponemes to the SflEp cells was either extremely poor or the 50% survival time (ST50) was less than 5 days. With two of these lots, no treponemes survived for 5 days. By contrast, in tests with 11 of the FBS lots, the ST50 of the treponemes was 12 days or greater; however, there was a great variation in the number of treponemes that attached. Selection of lots of FBS for ultimate experimental use was based on their influence both to extend length of time for survival of treponemes and to increase the number of treponemes that attached to the SflEp cells during that period.