The persistent form purification. Representative transmission electron micrographs of infected L929 cells (a) exposed or (b) unexposed to ampicillin and (c) the purified persistent form fraction containing aberrant RBs with a less electron dense appearance. Based on multiple cross-sections purified persistent form size is estimated at approximately 0.7–2.0 µm. Scale bars in (a) and (b) represent 2 µm and 0.5 µm in (c). (d) Endpoint infection assays determining IFUs on monolayers of L929 cells in each isolated density gradient fraction. Values represent mean IFU ± SD of three independent chlamydial preparations. (e) Representative images of the cell adherence assays demonstrating the inability of the persistent form to produce infection and inhibit cover slip adherence. Abbreviations: PF (+), persistent fraction purified from an infection exposed to ampicillin; PF (−) persistent fraction purified from an infection with no ampicillin exposure; RB (+), reticulate body fraction purified from an infection exposed to ampicillin; RB (−), reticulate body fraction purified from an infection with no ampicillin exposure; EB (+), elementary body fraction purified from an infection exposed to ampicillin; EB (−), elementary body fraction purified from an infection with no ampicillin exposure.