Cover photograph (Copyright © 2003, American Society for Microbiology. All Rights Reserved.): Fluorescence microscopy image illustrating heterologous cell-to-cell spread of Listeria monocytogenes. Bacteria (green) are spreading from a human-derived macrophage cell (CellTracker Blue-labeled cell on top) to a human-derived epithelial cell (cell at bottom). F-actin (red) of both host cells was labeled with Texas Red-X phalloidin, while bacteria were labeled by indirect immunofluorescence using an anti-Listeria primary antibody and a fluorescein-conjugated secondary antibody. (See related article on page 6295.)