Transmission electron microscopy (TEM) appearance of unexposed E. coli cells at (a) the low magnification (8000 ×, scale bar is 5 μm), (b) the middle magnification (20,000 ×, scale bar is 2 μm) and (c) the high magnification (40,000 ×, scale bar is 1 μm). (a) Representative distribution of different shapes of the bacteria, varying from spherical to elongate rod-shaped, depending on the cell cycle and their orientation in TEM section. Two newly divided cells (arrows) and regions of high- and low-electron density are visible with the middle magnification (b) Pili on the surfaces of the bacteria (arrow) are resolved with high magnification (c). Although the images are not quantitative, the surviving fraction as measured by colony formation was 1.00 by definition.