Cover photograph (Copyright © 1999, American Society for Microbiology. All rights reserved.): Agar diffusion assay showing the reversal of -lactam resistance of a -lactamase-producing strain of Escherichia coli by the murein hydrolase inhibitor bulgecin. The plate was seeded with E. coli harboring a plasmid that carries the ampC ampR genes from Enterobacter cloacae. The green filter strip was soaked with bulgecin (500 µg/ml), a specific inhibitor of the soluble lytic transglycosylase Slt70, and the red filter strip was soaked with cefoxitin (100 µg/ml). The strain shows resistance to cefoxitin but becomes sensitive in the presence of bulgecin, that is, at the intersection of both filter strips. (Photograph by Joachim-Volker Höltje, image processed with Adobe Photoshop.) (See related article on page 7192.)