title: vanA-containing Enterococcus faecium susceptible to vancomycin and teicoplanin because of major nucleotide deletions in Tn1546.
abstract: OBJECTIVE
  During the course of routine screening for vancomycin-resistant enterococci (VRE), we found six Enterococcus faecium isolates positive for vanA by PCR, but susceptible to vancomycin and teicoplanin by phenotypic testing. The aim of this study was to characterize the genetic composition of the Tn1546 vanA gene cluster of these isolates.
  
  
  METHODS
  The E. faecium isolates were characterized by antibiotic susceptibility, PFGE and structural analysis of the Tn1546 elements. Plasmids extracted from these isolates were used to determine the presence of the Tn1546 vanA gene cluster by PCR and the genomic organization of the deleted Tn1546 element by primer walking DNA sequencing.
  
  
  RESULTS
  The vancomycin-susceptible vanA-positive E. faecium isolates showed three PFGE patterns, and were missing the vanR and vanS genes that are responsible for the activation of transcription of resistance genes. Primer walking sequencing revealed that these genes were completely deleted and that interruptions in the vanA cluster were in the vicinity of insertion sequence elements.
  
  
  CONCLUSIONS
  The presence of vancomycin-susceptible vanA-positive E. faecium in clinical samples results from major deletions in the Tn1546 vanA operon. Our findings support the essential role of vanR and vanS for the expression of resistance to vancomycin in enterococci.
authors.affiliation: Département de Microbiologie et d'Infectiologie,  Centre Hospitalier de l'Université de Montréal, Montréal, Québec,  Canada.
authors.forename: Simon
authors.initials: S
authors.lastname: Gagnon
authors.forename: Simon
authors.initials: S
authors.lastname: Lévesque
authors.forename: Brigitte
authors.initials: B
authors.lastname: Lefebvre
authors.forename: Anne-Marie
authors.initials: AM
authors.lastname: Bourgault
authors.forename: Annie-Claude
authors.initials: AC
authors.lastname: Labbé
authors.forename: Michel
authors.initials: M
authors.lastname: Roger
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics*; D019729:Carbon-Oxygen Ligases / Q000235:genetics*; D004251:DNA Transposable Elements; D004269:DNA, Bacterial / Q000235:genetics; D016521:Electrophoresis, Gel, Pulsed-Field; D016984:Enterococcus faecium / Q000187:drug effects* / Q000235:genetics; D023061:Gene Order; D006801:Humans; D008826:Microbial Sensitivity Tests; D016133:Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D017384:Sequence Deletion; D017334:Teicoplanin / Q000494:pharmacology*; D014640:Vancomycin / Q000494:pharmacology*
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D004251:DNA Transposable Elements; D004269:DNA, Bacterial; C071437:VanA ligase, Bacteria; D017334:Teicoplanin; D014640:Vancomycin; D019729:Carbon-Oxygen Ligases