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Related Experiment Videos

Vancomycin-dependent Enterococcus faecalis clinical isolates and revertant mutants

F Van Bambeke1, M Chauvel, P E Reynolds

  • 1Unité des Agents Antibactériens, Institut Pasteur, 75724 Paris Cedex 15, France.

Antimicrobial Agents and Chemotherapy
|December 31, 1998
PubMed
Summary
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Vancomycin-dependent Enterococcus faecalis strains develop resistance through mutations in ddl or vanSB genes. This rapid reversion suggests interrupting vancomycin therapy may not cure infections.

Area of Science:

  • Microbiology
  • Molecular Biology
  • Genetics

Background:

  • Vancomycin-dependent Enterococcus faecalis (VdEnterococci) poses a treatment challenge.
  • The VanB resistance phenotype involves a two-component regulatory system activating the vanB operon.
  • Understanding resistance mechanisms is crucial for effective treatment strategies.

Purpose of the Study:

  • To investigate the genetic basis of vancomycin dependence and resistance in clinical Enterococcus faecalis isolates.
  • To analyze mutations in the ddl gene and the vanSB-vanRB regulatory system.
  • To characterize the peptidoglycan precursor synthesis under different antibiotic conditions.

Main Methods:

  • DNA sequencing of ddl, vanSB, and vanRB genes.
  • Reporter assays using DD-dipeptidase activity to measure resistance gene expression.

Related Experiment Videos

  • Analysis of peptidoglycan precursor synthesis.

    • Main Results:

    • Mutations in the ddl gene impaired host D-Ala:D-Ala ligase activity, leading to synthesis of D-Ala-D-Lac precursors.
    • Vancomycin-independent revertants showed restored D-Ala:D-Ala ligase activity (ddl mutations) or constitutive resistance (vanSB mutations).
    • Mutations in vanSB affected the sensor's autophosphorylation site or ATP binding domain, leading to constitutive or antibiotic-dependent resistance.

    Conclusions:

    • The ddl gene mutations are responsible for vancomycin dependence in these isolates.
    • Rapid in vitro emergence of vancomycin-independent revertants indicates potential treatment limitations.
    • Interruption of vancomycin therapy alone may be insufficient for curing VdEnterococci infections.