FIG 1 .

Antibiotics inhibiting essential PG synthesis enzymes or MreB activate the Cpx envelope stress response. (A) β-Lactams and A22 induce the expression of the specific CpxR activity reporter PcpxP-lacZ. Wild-type (GL43) and cpxR::kanR (GL73) cells were incubated with or without amdinocillin (mecillinam) (0.3 µg/ml), cephalexin (10 µg/ml), or A22 (5 µg/ml) for 1 h before measurement of β-galactosidase activity. A.U., arbitrary units. All values were normalized by the average activity obtained for untreated wild-type cells. Bars represent the average of normalized values from three independent clones. Error bars represent the standard error of the mean (SEM). (B) β-Lactams and A22 induce the expression of the specific Cpx reporter PcpxP-gfpmut2. Wild-type (GL368 [top]) and ΔcpxR (GL382 [bottom]) cells carrying the PcpxP-gfpmut2 reporter on a plasmid were incubated with or without amdinocillin or A22 as in panel A before imaging. (Left) distribution of total GFP fluorescence intensity per cell normalized by cell area obtained from cells displayed on the right. (Right) Phase-contrast and GFP fluorescence images of representative cells treated or not with amdinocillin or A22. (C) Relative growth inhibition zone around amdinocillin Sensi-Discs. The diameter of growth inhibition was measured around Sensi-Discs containing 10 µg amdinocillin after overnight incubation. Each value was normalized by the average diameter obtained for the control strain. Bar graphs represent averages ± SEM of normalized values from at least three biological replicates for each strain (GL43 [control] and GL73 on the left, GL63 [control] and GL62 on the right). For all panels, ** indicates P ≤ 0.01 and *** indicates P ≤ 0.001.