Format

Send to

Choose Destination
Proc Natl Acad Sci U S A. 2018 Oct 16;115(42):10786-10791. doi: 10.1073/pnas.1809285115. Epub 2018 Oct 1.

Copper inhibits peptidoglycan LD-transpeptidases suppressing β-lactam resistance due to bypass of penicillin-binding proteins.

Author information

1
Centre for Bacterial Cell Biology, Institute for Cell and Molecular Biosciences, Newcastle University, NE2 4AX Newcastle upon Tyne, United Kingdom.
2
Sorbonne Université, Sorbonne Paris Cité, Université Paris Descartes, Université Paris Diderot, INSERM, Centre de Recherche des Cordeliers, CRC, 75006 Paris, France.
3
Dipartimento di Scienze Farmacolgiche e Biomolecolari, Universita degli Studi di Milano, 20122 Milano, Italy.
4
Department of Chemistry, Indiana University, Bloomington, IN 47405.
5
Centre for Bacterial Cell Biology, Institute for Cell and Molecular Biosciences, Newcastle University, NE2 4AX Newcastle upon Tyne, United Kingdom; w.vollmer@ncl.ac.uk.

Abstract

The peptidoglycan (PG) layer stabilizes the bacterial cell envelope to maintain the integrity and shape of the cell. Penicillin-binding proteins (PBPs) synthesize essential 4-3 cross-links in PG and are inhibited by β-lactam antibiotics. Some clinical isolates and laboratory strains of Enterococcus faecium and Escherichia coli achieve high-level β-lactam resistance by utilizing β-lactam-insensitive LD-transpeptidases (LDTs) to produce exclusively 3-3 cross-links in PG, bypassing the PBPs. In E. coli, other LDTs covalently attach the lipoprotein Lpp to PG to stabilize the envelope and maintain the permeability barrier function of the outermembrane. Here we show that subminimal inhibitory concentration of copper chloride sensitizes E. coli cells to sodium dodecyl sulfate and impair survival upon LPS transport stress, indicating reduced cell envelope robustness. Cells grown in the presence of copper chloride lacked 3-3 cross-links in PG and displayed reduced covalent attachment of Braun's lipoprotein and reduced incorporation of a fluorescent d-amino acid, suggesting inhibition of LDTs. Copper dramatically decreased the minimal inhibitory concentration of ampicillin in E. coli and E. faecium strains with a resistance mechanism relying on LDTs and inhibited purified LDTs at submillimolar concentrations. Hence, our work reveals how copper affects bacterial cell envelope stability and counteracts LDT-mediated β-lactam resistance.

KEYWORDS:

Enterococcus faecium; Escherichia coli; LD-transpeptidase; copper; peptidoglycan

PMID:
30275297
PMCID:
PMC6196517
DOI:
10.1073/pnas.1809285115
[Indexed for MEDLINE]
Free PMC Article

Supplemental Content

Full text links

Icon for HighWire Icon for PubMed Central
Loading ...
Support Center