title: Novel mechanism of beta-lactam resistance due to bypass of DD-transpeptidation in Enterococcus faecium.
abstract: The peptidoglycan structure of in vitro selected ampicillin-resistant mutant Enterococcus faecium D344M512 and of the susceptible parental strain D344S was determined by reverse phase high performance liquid chromatography and mass spectrometry. The muropeptide monomers were almost identical in the two strains. The substantial majority (99.3%) of the oligomers from the susceptible strain D344S contained the usual d-alanyl --> d-asparaginyl (or d-aspartyl)-l-lysyl cross-link (d-Ala --> d-Asx-l-Lys) generated by beta-lactam-sensitive DD-transpeptidation. The remaining oligomers (0.7%) were produced by beta-lactam-insensitive LD-transpeptidation, because they contained l-Lys --> d-Asx-l-Lys cross-links. The muropeptide oligomers of the ampicillin-resistant mutant D344M512 contained only these l-Lys --> d-Asx-l-Lys cross-links indicating that resistance was due to the bypass of the beta-lactam-sensitive DD-transpeptidation reaction. The discovery of this novel resistance mechanism indicates that DD-transpeptidases cannot be considered anymore as the sole essential transpeptidase enzymes.
authors.affiliation: L.R.M.A., UFR Broussais-Hôtel Dieu, Université Paris VI, 75270 Paris, France. jlmainar@bhdc.jussieu.fr
authors.forename: J L
authors.initials: JL
authors.lastname: Mainardi
authors.forename: R
authors.initials: R
authors.lastname: Legrand
authors.forename: M
authors.initials: M
authors.lastname: Arthur
authors.forename: B
authors.initials: B
authors.lastname: Schoot
authors.forename: J
authors.initials: J
authors.lastname: van Heijenoort
authors.forename: L
authors.initials: L
authors.lastname: Gutmann
mesh_terms: D000595:Amino Acid Sequence; D000667:Ampicillin / Q000494:pharmacology*; D001426:Bacterial Proteins; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D019281:Dimerization; D016984:Enterococcus faecium / Q000187:drug effects* / Q000378:metabolism; D006602:Hexosyltransferases; D013058:Mass Spectrometry; D002267:Muramoylpentapeptide Carboxypeptidase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D046915:Penicillin-Binding Proteins; D010455:Peptides / Q000737:chemistry; D010457:Peptidoglycan / Q000737:chemistry; D010458:Peptidyl Transferases; D011487:Protein Conformation; D018440:beta-Lactam Resistance
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins; D046915:Penicillin-Binding Proteins; D010455:Peptides; D010457:Peptidoglycan; D000667:Ampicillin; D010458:Peptidyl Transferases; D006602:Hexosyltransferases; D002267:Muramoylpentapeptide Carboxypeptidase