Cover photograph (Copyright © 2013, American Society for Microbiology. All Rights Reserved.): The role of natural killer (NK) cells during enteric infection was determined using C57BL/6 mice treated with anti-asialo GM1 (to deplete NK cells) or control IgG every 3 or 4 days. These mice were then infected with lux-tagged (i.e., light-producing) Citrobacter rodentium (the murine pathogen related to human diarrheagenic Escherichia coli). On day 7 postinfection, in vivo whole-body bioluminescent images were captured and displayed as pseudocolor images (IgG control [left]; NK cell depleted [right]). Red represents the most-intense light emission, while blue corresponds to the weakest signal. Images were processed using LivingImage software 2.50 and falsely colored using GIMP 2 software. (See related article on p. 460.)