Electron microscopy of 042 and mutants. (a) Immunogold transmission electron microscopy for Aap protein. Black arrows indicate surface protein detected by anti-Aap antibody. Strains examined by scanning electron microscopy are 042 (b and c), 042aafA (d), 042aap (e–g), and 042aap(pAap) (h). In i, 042aap was incubated with 3 mg/ml purified Aap protein prior to fixing and staining. White arrows indicate AAF fimbriae in all specimens. All bars indicate 1 μm.