FIG 5.

S. marcescens peptidoglycan amidohydrolase deletions lead to differential derepression of ampC. (A) Phylogenetic analysis performed using the maximum-likelihood method and a JTT matrix-based model in MEGA X (30). An unrooted tree with the lowest log likelihood (−4,913) is shown. (B) Clarified sonicates from the indicated strains were incubated with equal amounts of nitrocefin, a chromogenic cephalosporin β-lactam, and absorbance was measured in the kinetic mode for 10 min. The slope of the line from the first 5 data points was used to calculate β-lactamase (βLA) activity, which was then normalized to the Wt, which corresponds to 31.2 nmol nitrocefin/min/mg total protein. Measurements are shown without preinduction and with induction with 4 μg/ml cefoxitin for 2 h prior to harvesting. The data represent the means and SEM of the results of 4 independent experiments. Comparisons were made between all uninduced mutants and the Wt and between each induced sample and its uninduced control. *, P < 0.05 after performance of the Bonferroni correction. All the induced samples were also significantly different from the corresponding uninduced samples, except for the ΔampD ΔamiD and ΔampD ΔamiD2 mutants and the triple mutant (these asterisks are not shown for clarity).