FIG. 4.

Transmission electron micrograph of immunogold-labeled IpaD at the tip of negatively stained needles. (A) Shigella isolates were grown to mid-log phase, harvested, and applied to carbon/Formvar-coated copper grids. They were then treated with rabbit anti-IpaD IgG and detected with 5 nm gold-labeled goat anti-rabbit IgG. Uranyl acetate (2%) was used for negative staining. (B) Needles were sheared from the Shigella, applied to carbon/Formvar-coated copper grids and treated as described above for panel A. (C) The Shigella strain mxiH/pRK2/SH116, which makes long needle, was treated as described for panel A. (D) Long needles (≥300 nm) were sheared from mxiH/pRK2/SH116 and treated as described above for panel A. Magnification, ×120,000.