title: Novel mechanism of resistance to glycopeptide antibiotics in Enterococcus faecium.
abstract: Glycopeptides and beta-lactams are the major antibiotics available for the treatment of infections due to Gram-positive bacteria. Emergence of cross-resistance to these drugs by a single mechanism has been considered as unlikely because they inhibit peptidoglycan polymerization by different mechanisms. The glycopeptides bind to the peptidyl-D-Ala(4)-D-Ala(5) extremity of peptidoglycan precursors and block by steric hindrance the essential glycosyltransferase and D,D-transpeptidase activities of the penicillin-binding proteins (PBPs). The beta-lactams are structural analogues of D-Ala(4)-D-Ala(5) and act as suicide substrates of the D,D-transpeptidase module of the PBPs. Here we have shown that bypass of the PBPs by the recently described beta-lactam-insensitive L,D-transpeptidase from Enterococcus faecium (Ldt(fm)) can lead to high level resistance to glycopeptides and beta-lactams. Cross-resistance was selected by glycopeptides alone or serially by beta-lactams and glycopeptides. In the corresponding mutants, UDP-MurNAc-pentapeptide was extensively converted to UDP-MurNAc-tetrapeptide following hydrolysis of D-Ala(5), thereby providing the substrate of Ldt(fm). Complete elimination of D-Ala(5), a residue essential for glycopeptide binding, was possible because Ldt(fm) uses the energy of the L-Lys(3)-D-Ala(4) peptide bond for cross-link formation in contrast to PBPs, which use the energy of the D-Ala(4)-D-Ala(5) bond. This novel mechanism of glycopeptide resistance was unrelated to the previously identified replacement of D-Ala(5) by D-Ser or D-lactate.
authors.affiliation: INSERM U655-LRMA, Centre de Recherches Biomédicales des Cordeliers, Université Paris 6, 15 Rue de l'Ecole de Médecine, Paris 75270, France.
authors.forename: Julie
authors.initials: J
authors.lastname: Cremniter
authors.forename: Jean-Luc
authors.initials: JL
authors.lastname: Mainardi
authors.forename: Nathalie
authors.initials: N
authors.lastname: Josseaume
authors.forename: Jean-Charles
authors.initials: JC
authors.lastname: Quincampoix
authors.forename: Lionel
authors.initials: L
authors.lastname: Dubost
authors.forename: Jean-Emmanuel
authors.initials: JE
authors.lastname: Hugonnet
authors.forename: Arul
authors.initials: A
authors.lastname: Marie
authors.forename: Laurent
authors.initials: L
authors.lastname: Gutmann
authors.forename: Louis B
authors.initials: LB
authors.lastname: Rice
authors.forename: Michel
authors.initials: M
authors.lastname: Arthur
mesh_terms: D000409:Alanine / Q000378:metabolism; D019943:Amino Acid Substitution; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D003432:Cross-Linking Reagents / Q000494:pharmacology; D003593:Cytoplasm / Q000378:metabolism; D024881:Drug Resistance, Bacterial; D016984:Enterococcus faecium / Q000235:genetics / Q000378:metabolism*; D006020:Glycopeptides / Q000494:pharmacology*; D006868:Hydrolysis; D008826:Microbial Sensitivity Tests; D008954:Models, Biological; D002267:Muramoylpentapeptide Carboxypeptidase / Q000378:metabolism; D010446:Peptide Fragments / Q000737:chemistry; D010457:Peptidoglycan / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism; D013379:Substrate Specificity; D047090:beta-Lactams / Q000378:metabolism
chemical_list: D000900:Anti-Bacterial Agents; D003432:Cross-Linking Reagents; D006020:Glycopeptides; D010446:Peptide Fragments; D010457:Peptidoglycan; D047090:beta-Lactams; D002267:Muramoylpentapeptide Carboxypeptidase; D000409:Alanine