Inhibition of Peptidoglycan Cross-Linking in Growing Cells of Escherichia coli by Penicillins and Cephalosporins, and Its Prevention by R Factor-Mediated Beta-Lactamase

Abstract

The degree of peptidoglycan cross-linking has been studied in growing cells of a Dap-Lys-auxotroph of Escherichia coli K-12 by following the incorporation of [3H]diaminopimelic acid into the lysozyme digestion products of crude, isolated peptidoglycan. The percentage of inhibition of cross-linking increases with increasing concentrations of penicillin G, cephaloridine, and cefuroxime. When the R factor Rldrd 19 was introduced into the strain by conjugation, it was found that the type IHa, /8-lactamase specified by the plasmid was able to protect the cross-linking target against inhibition by penicillin G but not against cephaloridine, even though the f3-lactamase hydrolyzes this substrate 50% faster than penicillin G. Cefuroxime, which is completely resistant to hydrolysis by the type IlIa ,B-lactamase, inhibited the peptidoglycan cross-linking target in both the RI and R-variants of the assay strain. A mutant plasmid, Rldrdl9amp2, which specified no type IIIa f8-lactamase synthesis, could not provide protection of the cross-linking target against penicillin G. The significance of these results, in relation to the ability of the antibiotics to pass the permeability barrier of the bacterial envelope, is discussed.

Inhibition of Escherichia coli K-12 by β-Lactam Antibiotics With Poor Antibacterial Activity: Interaction of Permeability And Intrinsic Activity Against Penicillin-Binding Proteins

“…Cephaloridine, on the other hand, is equally active against the PBPs of both E. coli strains and has the same activity against intact bacteria of both strains, indicating that this derivative has little difficulty penetrating to the target, a result substantiated by other work (3,16,17). DISCUSSION The results described in this paper show that the lack of antibacterial activity of methicillin, cloxacilhin, 1078/1/1 and, to a lesser extent, penicillin G against non-f-lactamase-producing strains of E. coli K-12 is due to impenetrability of the compounds through the outer membrane of the bacterial envelope.…”

Transition state structures of a dipeptide related to the mode of action of beta-lactam antibiotics.

“…The final step in cell wall synthesis, the crosslinking of the peptidoglycan strands via a transpeptidation reaction, is the one that is upset by penicillins and cephalosporins. Depending on the organism and the antibiotic, the inhibition can involve a transpeptidase or a carboxypeptidase, be reversible or irreversible, and lead either directly or indirectly to death of growing bacteria (2,4,(8)(9)(10)(11)(12)(13)(14)(15)(16). In bacteria that have been studied (2), the peptidoglycan crosslinks are polypeptides which in their precursor form have.…”