Reversible vancomycin susceptibility within emerging ST1421 Enterococcus faecium strains is associated with rearranged vanA-gene clusters and increased vanA plasmid copy number

Theresa Maria Wagner; Jessin Janice; Mark Schulz; Susan A Ballard; Anders Goncalves da Silva; Geoffrey W Coombs; Denise A Daley; Stanley Pang; Shakeel Mowlaboccus; Tim Stinear; Kristin Hegstad; Benjamin P Howden; Arnfinn Sundsfjord

doi:10.1016/j.ijantimicag.2023.106849

Reversible vancomycin susceptibility within emerging ST1421 Enterococcus faecium strains is associated with rearranged vanA-gene clusters and increased vanA plasmid copy number

Int J Antimicrob Agents. 2023 Jul;62(1):106849. doi: 10.1016/j.ijantimicag.2023.106849. Epub 2023 May 13.

Affiliations

¹ Research group for Host-Microbe Interactions, Department of Medical Biology, Faculty of Health Sciences, UiT The Arctic University of Norway, Tromsø, Norway.
² Research group for Host-Microbe Interactions, Department of Medical Biology, Faculty of Health Sciences, UiT The Arctic University of Norway, Tromsø, Norway; Norwegian National Advisory Unit on Detection of Antimicrobial Resistance, Department of Microbiology and Infection Control, University Hospital of North Norway, Tromsø, Norway.
³ The Microbiological Diagnostic Unit Public Health Laboratory and Doherty Applied Microbial Genomics, Department of Microbiology and Immunology, University of Melbourne, Doherty Institute for Infection and Immunity, Melbourne, Victoria 3000, Australia.
⁴ Antimicrobial Resistance and Infectious Disease (AMRID) Research Laboratory, Murdoch University, Murdoch, Western Australia, Australia; Department of Microbiology, PathWest Laboratory Medicine-WA, Fiona Stanley Hospital, Murdoch, Western Australia, Australia.
⁵ Australian Group on Antimicrobial Resistance, Fiona Stanley Hospital, Murdoch, Western Australia, Australia.
⁶ The Microbiological Diagnostic Unit Public Health Laboratory and Doherty Applied Microbial Genomics, Department of Microbiology and Immunology, University of Melbourne, Doherty Institute for Infection and Immunity, Melbourne, Victoria 3000, Australia; Department of Infectious Diseases, Austin Health, Heidelberg, Victoria, Australia. Electronic address: bhowden@unimelb.edu.au.
⁷ Research group for Host-Microbe Interactions, Department of Medical Biology, Faculty of Health Sciences, UiT The Arctic University of Norway, Tromsø, Norway; Norwegian National Advisory Unit on Detection of Antimicrobial Resistance, Department of Microbiology and Infection Control, University Hospital of North Norway, Tromsø, Norway; The Microbiological Diagnostic Unit Public Health Laboratory and Doherty Applied Microbial Genomics, Department of Microbiology and Immunology, University of Melbourne, Doherty Institute for Infection and Immunity, Melbourne, Victoria 3000, Australia. Electronic address: arnfinn.sundsfjord@uit.no.

PMID: 37187337
DOI: 10.1016/j.ijantimicag.2023.106849

Abstract

Vancomycin variable enterococci (VVE) are van-positive enterococci with a vancomycin-susceptible phenotype (VVE-S) that can convert to a resistant phenotype (VVE-R) and be selected for during vancomycin exposure. VVE-R outbreaks have been reported in Canada and Scandinavian countries. The aim of this study was to examine the presence of VVE in whole genome sequenced (WGS) Australian bacteremia Enterococcus faecium (Efm) isolates collected through the Australian Group on Antimicrobial resistance (AGAR) network. Eight potential VVEAus isolates, all identified as Efm ST1421, were selected based on the presence of vanA and a vancomycin-susceptible phenotype. During vancomycin selection, two potential VVE-S harboring intact vanHAX genes, but lacking the prototypic vanRS and vanZ genes, reverted to a resistant phenotype (VVEAus-R). Spontaneous VVEAus-R reversion occurred at a frequency of 4-6 × 10^-8 resistant colonies per parent cell in vitro after 48 h and led to high-level vancomycin and teicoplanin resistance. The S to R reversion was associated with a 44-bp deletion in the vanHAX promoter region and an increased vanA plasmid copy number. The deletion in the vanHAX promoter region enables an alternative constitutive promoter for the expression of vanHAX. Acquisition of vancomycin resistance was associated with a low fitness cost compared with the corresponding VVEAus-S isolate. The relative proportion of VVEAus-R vs. VVEAus-S decreased over time in serial passages without vancomycin selection. Efm ST1421 is one of the predominant VanA-Efm multilocus sequence types found across most regions of Australia, and has also been associated with a major prolonged VVE outbreak in Danish hospitals.

Keywords: Enterococcus faecium; Teicoplanin; VRE; Vancomycin; Vancomycin variable.

MeSH terms

Anti-Bacterial Agents / pharmacology
Australia / epidemiology
Bacterial Proteins / genetics
DNA Copy Number Variations
Enterococcus / genetics
Enterococcus faecium* / genetics
Gram-Positive Bacterial Infections* / epidemiology
Humans
Multigene Family
Plasmids / genetics
Vancomycin / pharmacology

Substances

Vancomycin
Anti-Bacterial Agents
Bacterial Proteins