title: Vancomycin-variable enterococci can give rise to constitutive resistance during antibiotic therapy.
abstract: Vancomycin-resistant enterococci (VRE) are notorious clinical pathogens restricting the use of glycopeptide antibiotics in the clinic setting. Routine surveillance to detect VRE isolated from patients relies on PCR bioassays and chromogenic agar-based test methods. In recent years, we and others have reported the emergence of enterococcal strains harboring a "silent" copy of vancomycin resistance genes that confer a vancomycin-susceptible phenotype (vancomycin-susceptible enterococci [VSE]) and thus escape detection using drug sensitivity screening tests. Alarmingly, these strains are able to convert to a resistance phenotype (VSE→VRE) during antibiotic treatment, severely compromising the success of therapy. Such strains have been termed vancomycin-variable enterococci (VVE). We have investigated the molecular mechanisms leading to the restoration of resistance in VVE isolates through the whole-genome sequencing of resistant isolates, measurement of resistance gene expression, and quantification of the accumulation of drug-resistant peptidoglycan precursors. The results demonstrate that VVE strains can revert to a VRE phenotype through the constitutive expression of the vancomycin resistance cassette. This is accomplished through a variety of changes in the DNA region upstream of the resistance genes that includes both a deletion of a likely transcription inhibitory secondary structure and the introduction of a new unregulated promoter. The VSE→VRE transition of VVE can occur in patients during the course of antibiotic therapy, resulting in treatment failure. These VVE strains therefore pose a new challenge to the current regimen of diagnostic tests used for VRE detection in the clinic setting.
authors.affiliation: M. G. DeGroote Institute for Infectious Disease Research, Department of Biochemistry and Biomedical Sciences and the Department of Chemistry, McMaster University, Hamilton, Ontario, Canada.
authors.forename: Maulik N
authors.initials: MN
authors.lastname: Thaker
authors.affiliation: M. G. DeGroote Institute for Infectious Disease Research, Department of Biochemistry and Biomedical Sciences and the Department of Chemistry, McMaster University, Hamilton, Ontario, Canada.
authors.forename: Lindsay
authors.initials: L
authors.lastname: Kalan
authors.affiliation: M. G. DeGroote Institute for Infectious Disease Research, Department of Biochemistry and Biomedical Sciences and the Department of Chemistry, McMaster University, Hamilton, Ontario, Canada.
authors.forename: Nicholas
authors.initials: N
authors.lastname: Waglechner
authors.affiliation: Public Health Ontario, Public Health Laboratory, Toronto, Canada.
authors.forename: Alireza
authors.initials: A
authors.lastname: Eshaghi
authors.affiliation: Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Canada Public Health Ontario, Public Health Laboratory, Toronto, Canada.
authors.forename: Samir N
authors.initials: SN
authors.lastname: Patel
authors.affiliation: Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Canada Division of Infectious Diseases, University of Toronto, Toronto, Canada Department of Microbiology, University Health Network/Mount Sinai Hospital, Toronto, Canada.
authors.forename: Susan
authors.initials: S
authors.lastname: Poutanen
authors.affiliation: Department of Microbiology, University Health Network/Mount Sinai Hospital, Toronto, Canada.
authors.forename: Barbara
authors.initials: B
authors.lastname: Willey
authors.affiliation: Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Canada Division of Infectious Diseases, University of Toronto, Toronto, Canada Department of Microbiology, University Health Network/Mount Sinai Hospital, Toronto, Canada.
authors.forename: Bryan
authors.initials: B
authors.lastname: Coburn
authors.affiliation: Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Canada Division of Infectious Diseases, University of Toronto, Toronto, Canada Department of Microbiology, University Health Network/Mount Sinai Hospital, Toronto, Canada.
authors.forename: Allison
authors.initials: A
authors.lastname: McGeer
authors.affiliation: Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Canada Division of Infectious Diseases, University of Toronto, Toronto, Canada Department of Microbiology, University Health Network/Mount Sinai Hospital, Toronto, Canada.
authors.forename: Donald E
authors.initials: DE
authors.lastname: Low
authors.affiliation: M. G. DeGroote Institute for Infectious Disease Research, Department of Biochemistry and Biomedical Sciences and the Department of Chemistry, McMaster University, Hamilton, Ontario, Canada wrightge@mcmaster.ca.
authors.forename: Gerard D
authors.initials: GD
authors.lastname: Wright
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics; D019729:Carbon-Oxygen Ligases / Q000235:genetics; D016983:Enterococcus / Q000187:drug effects* / Q000302:isolation & purification; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic; D014640:Vancomycin / Q000494:pharmacology*; D020713:Vancomycin Resistance
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; C071437:VanA ligase, Bacteria; C070700:VanH protein, Enterococcus faecium; D014640:Vancomycin; D019729:Carbon-Oxygen Ligases