Motility parameters associated with <i>Treponema pallidum</i>-platelet interactions.

The movement and cell characteristics were contrasted between platelet-interacting (shaded circles) and non-interacting (open circles) treponemes utilizing high-resolution darkfield videos at 1000x magnification. (A) Treponeme wavelength (green bracket) and amplitude (yellow bracket) were measured only when the cell body waveform was in the plane of focus (grey bracket). Two activated platelets (white arrowheads) are bound by one treponeme. The grey bracket shows a segment of the treponeme with cell peak and troughs in the same focal plane. (B) Treponeme length was measured when the full treponeme was in the same focal plane (magenta bracket). (C) Platelet-interacting treponemes demonstrated a higher translational velocity (mean = 1.68 ± 0.10 μm/sec [SEM] *P < 0.0001, n = 24) compared with non-interacting treponemes (mean = 0.65 ± 0.10 μm/sec [SEM], n = 12). (D) Frame by frame analysis determined platelet-interacting treponemes rotate at a higher frequency (mean = 2.60 ± 0.27 Hz [SEM] **P = 0.0060, n = 12) versus non-interacting treponemes (mean = 1.46 ± 0.25 Hz [SEM], n = 11). (E) Top panel: Platelet-interacting treponemes maintained a more tightly coiled helix resulting in a shorter wavelength (mean = 0.79 ± 0.02 μm [SEM] ***P = 0.0237) versus non-interacting treponemes (mean = 0.86 ± 0.02 μm [SEM]), n = 15. Middle panel: Platelet-interacting treponemes demonstrated a trend towards a higher amplitude (mean = 0.30 ± 0.02 μm [SEM]) compared with non-interacting treponemes (mean = 0.27 ± 0.01 μm [SEM]), n = 15. Bottom panel: Platelet-interacting treponemes also displayed a trend towards a shorter, more compact coiled shape (mean cell length = 9.56 ± 0.65 μm [SEM]) compared with non-interacting treponemes (mean cell length = 10.46 ± 0.66 μm [SEM]), n = 15. Student’s unpaired two-tailed t tests were used to calculate statistical significance. Scale bars = 5 μm.