title: Mutations leading to increased levels of resistance to glycopeptide antibiotics in VanB-type enterococci.
abstract: The vanB gene cluster mediates glycopeptide resistance by production of peptidoglycan precursors ending in the depsipeptide D-alanyl-D-lactate (D-Ala-D-Lac) instead of D-Ala-D-Ala found in susceptible enterococci. Synthesis of D-Ala-D-Lac and hydrolysis of D-Ala-D-Ala is controlled by the VanR(B)S(B) two-component regulatory system that activates transcription of the resistance genes in response to vancomycin but not to teicoplanin. Two substitutions (A3C-->G or D168-->Y) in the VanS(B) sensor kinase resulted in induction by teicoplanin, indicating that the N-terminal domain of the protein was involved in glycopeptide sensing. A substitution (T237-->K) located in the vicinity of the putative autophosphorylation site of VanS(B) (H233) was associated with a constitutive phenotype and affected a conserved residue known to be critical for the phosphatase activity of related kinases. A mutant producing an impaired host D-Ala:D-Ala ligase required vancomycin for growth, since D-Ala-D-Lac was only produced under inducing conditions. The ddl and vanS(B) mutations, alone or in combination, resulted in various resistance phenotypes that were determined by the amount of D-Ala-D-Ala and D-Ala-D-Lac incorporated into peptidoglycan precursors under different inducing conditions.
authors.affiliation: Unité des Agents Antibactériens, Centre National de la Recherche Scientifique EP J0058, Institut Pasteur, Paris, France.
authors.forename: M
authors.initials: M
authors.lastname: Baptista
authors.forename: F
authors.initials: F
authors.lastname: Depardieu
authors.forename: P
authors.initials: P
authors.lastname: Reynolds
authors.forename: P
authors.initials: P
authors.lastname: Courvalin
authors.forename: M
authors.initials: M
authors.lastname: Arthur
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001426:Bacterial Proteins / Q000235:genetics*; D024881:Drug Resistance, Bacterial / Q000235:genetics*; D016983:Enterococcus / Q000187:drug effects / Q000235:genetics*; D008826:Microbial Sensitivity Tests; D009154:Mutation; D010453:Peptide Synthases / Q000032:analysis; D017334:Teicoplanin / Q000494:pharmacology; D014161:Transduction, Genetic; D020713:Vancomycin Resistance / Q000235:genetics*
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; C079913:VanB protein, Enterococcus; D017334:Teicoplanin; D010453:Peptide Synthases; C019638:D-alanylalanine synthetase