Enumeration of Treponema pallidum cells cultivated in vitro by an enzyme-linked immunosorbent assay.

An enzyme-linked immunosorbent assay was developed to enumerate Treponema pallidum cells. The assay could detect from 2 X 10(7) to 4 X 10(8) treponemes per ml. Reactive rabbit serum and goat anti-rabbit immunoglobulin G (peroxidase conjugate) were used in the assay. Optimum results were obtained when 2,2'-azino-di(ethylbenzthiazolinesulfonic acid) was used as the dye for the enzyme reaction and the reactions were allowed to run for 45 min. Interestingly, assays in which in vivo-cultivated T. pallidum was used produced lower absorbance values than those in which T. pallidum was cultivated in vitro.