(a) Muropeptide composition of the peptidoglycan of strains BW25113∆6ldt, M1.5, and BW25113 ‘wild-type’. aData are the mean ± standard deviation from independent experiments (see note c). bβ-Lactam added to the growth medium. AZT, aztreonam at 12 µg/mL; MEC, mecillinam at 2.5 µg/mL; AMP, ampicillin at 16 µg/mL. cThe number of independent peptidoglycan analyses is indicated in parenthesis. Abbreviations: ND, not detected; Tri, tripeptide monomer; Tetra, tetrapeptide monomer; Penta, pentapeptide monomer; Tri→Tri, Tri→Tetra, and Tri→Penta, 3→3 cross-linked dimers; Tetra→Tri and Tetra→Tetra, 4→3 cross-linked dimers. The inter-peptide cross-link direction is indicated using the donor→acceptor conventional notation. (b) Generation time for growth of BW25113 derivatives in M1 minimal medium aβ-lactam added to the growth medium. AZT, aztreonam at 12 µg/mL; MEC, mecillinam at 2.5 µg/mL; AMP, ampicillin at 16 µg/mL. bFor growth in the presence of aztreonam and mecillinam, the values were deduced from the variation in OD600 during 90 min. (c) Susceptibility of Escherichia coli strains to β-lactams. Data are the medians from six experiments.