Transmission electron microscopy appearance of E. coli cells from the 5-mL, 5-min exposure treatment combination. At the low magnification (a) (20,000 ×, scale bar is 2 μm), nearly all cells are seen as damaged and missing cytoplasm to various extents; many cell wall fragments are evident. In another field of view (b) (25,000 ×, scale bar is 2 μm), three apparently intact cells share the optical field with three damaged cells and many cellular fragments. The high magnification view (c) (40,000 ×, scale bar is 1 μm) of a smaller portion of the optical field in (b) shows an electron-dense cell essentially indistinguishable from those in unexposed cell images (Fig. 6), a cell in which the cell wall in this plane of section appears intact but the cell is almost free of cytoplasm, and a cell in which an approximately 120-nm hole exists. No pili remain on the bacterial surfaces. The surviving fraction associated with this treatment combination was 0.26 ± 0.07.