title: Vancomycin and oritavancin have different modes of action in Enterococcus faecium.
abstract: The increasing frequency of Enterococcus faecium isolates with multidrug resistance is a serious clinical problem given the severely limited number of therapeutic options available to treat these infections. Oritavancin is a promising new alternative in clinical development that has potent antimicrobial activity against both staphylococcal and enterococcal vancomycin-resistant pathogens. Using solid-state NMR to detect changes in the cell-wall structure and peptidoglycan precursors of whole cells after antibiotic-induced stress, we report that vancomycin and oritavancin have different modes of action in E. faecium. Our results show the accumulation of peptidoglycan precursors after vancomycin treatment, consistent with transglycosylase inhibition, but no measurable difference in cross-linking. In contrast, after oritavancin exposure, we did not observe the accumulation of peptidoglycan precursors. Instead, the number of cross-links is significantly reduced, showing that oritavancin primarily inhibits transpeptidation. We propose that the activity of oritavancin is the result of a secondary binding interaction with the E. faecium peptidoglycan. The hypothesis is supported by results from (13)C{(19)F} rotational-echo double-resonance (REDOR) experiments on whole cells enriched with l-[1-(13)C]lysine and complexed with desleucyl [(19)F]oritavancin. These experiments establish that an oritavancin derivative with a damaged d-Ala-d-Ala binding pocket still binds to E. faecium peptidoglycan. The (13)C{(19)F} REDOR dephasing maximum indicates that the secondary binding site of oritavancin is specific to nascent and template peptidoglycan. We conclude that the inhibition of transpeptidation by oritavancin in E. faecium is the result of the large number of secondary binding sites relative to the number of primary binding sites.
authors: Department of Chemistry, Washington University, One Brookings Drive, St. Louis, MO 63130, USA.
authors: Gary J
authors: GJ
authors: Patti
authors: Sung Joon
authors: SJ
authors: Kim
authors: Tsyr-Yan
authors: TY
authors: Yu
authors: Evelyne
authors: E
authors: Dietrich
authors: Kelly S E
authors: KS
authors: Tanaka
authors: Thomas R
authors: TR
authors: Parr
authors: Adel Rafai
authors: AR
authors: Far
authors: Jacob
authors: J
authors: Schaefer
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002247:Carbon Isotopes / Q000378:metabolism; D002473:Cell Wall / Q000737:chemistry / Q000187:drug effects; D016984:Enterococcus faecium / Q000737:chemistry / Q000187:drug effects*; D005461:Fluorine / Q000378:metabolism; D006020:Glycopeptides / Q000494:pharmacology*; D000077427:Lipoglycopeptides; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D015394:Molecular Structure; D010457:Peptidoglycan / Q000378:metabolism; D014640:Vancomycin / Q000494:pharmacology* / Q000031:analogs & derivatives
chemical_list: D000900:Anti-Bacterial Agents; D002247:Carbon Isotopes; D006020:Glycopeptides; D000077427:Lipoglycopeptides; D010457:Peptidoglycan; D005461:Fluorine; D014640:Vancomycin; C100708:oritavancin