title: A multicentre hospital outbreak in Sweden caused by introduction of a vanB2 transposon into a stably maintained pRUM-plasmid in an Enterococcus faecium ST192 clone.
abstract: The clonal dissemination of VanB-type vancomycin-resistant Enterococcus faecium (VREfm) strains in three Swedish hospitals between 2007 and 2011 prompted further analysis to reveal the possible origin and molecular characteristics of the outbreak strain. A representative subset of VREfm isolates (n = 18) and vancomycin-susceptible E. faecium (VSEfm, n = 2) reflecting the spread in time and location was approached by an array of methods including: selective whole genome sequencing (WGS; n = 3), multi locus sequence typing (MLST), antimicrobial susceptibility testing, virulence gene profiling, identification of mobile genetic elements conferring glycopeptide resistance and their ability to support glycopeptide resistance transfer. In addition, a single VREfm strain with an unrelated PFGE pattern collected prior to the outbreak was examined by WGS. MLST revealed a predominance of ST192, belonging to a hospital adapted high-risk lineage harbouring several known virulence determinants (n≥10). The VREfm outbreak strain was resistant to ampicillin, gentamicin, ciprofloxacin and vancomycin, and susceptible to teicoplanin. Consistently, a vanB2-subtype as part of Tn1549/Tn5382 with a unique genetic signature was identified in the VREfm outbreak strains. Moreover, Southern blot hybridisation analyses of PFGE separated S1 nuclease-restricted total DNAs and filter mating experiments showed that vanB2-Tn1549/Tn5382 was located in a 70-kb sized rep17/pRUM plasmid readily transferable between E. faecium. This plasmid contained an axe-txe toxin-antitoxin module associated with stable maintenance. The two clonally related VSEfm harboured a 40 kb rep17/pRUM plasmid absent of the 30 kb vanB2-Tn1549/Tn5382 gene complex. Otherwise, these two isolates were similar to the VREfm outbreak strain in virulence- and resistance profile. In conclusion, our observations support that the origin of the multicentre outbreak was caused by an introduction of vanB2-Tn1549/Tn5382 into a rep17/pRUM plasmid harboured in a pre-existing high-risk E. faecium ST192 clone. The subsequent dissemination of VREfm to other centres was primarily caused by clonal spread rather than plasmid transfer to pre-existing high-risk clones.
authors.affiliation: Research group for Host-Microbe Interactions, Faculty of Health Sciences, University of Tromsø - The Arctic University of Norway, Tromsø, Norway.
authors.forename: Audun
authors.initials: A
authors.lastname: Sivertsen
authors.affiliation: Unit for antibiotics and infection control, the Public Health Agency of Sweden, Solna, Sweden.
authors.forename: Hanna
authors.initials: H
authors.lastname: Billström
authors.affiliation: Unit for antibiotics and infection control, the Public Health Agency of Sweden, Solna, Sweden.
authors.forename: Öjar
authors.initials: Ö
authors.lastname: Melefors
authors.affiliation: Unit for antibiotics and infection control, the Public Health Agency of Sweden, Solna, Sweden.
authors.forename: Barbro Olsson
authors.initials: BO
authors.lastname: Liljequist
authors.affiliation: Unit for antibiotics and infection control, the Public Health Agency of Sweden, Solna, Sweden.
authors.forename: Karin Tegmark
authors.initials: KT
authors.lastname: Wisell
authors.affiliation: Department of Clinical Microbiology, Karolinska University Hospital, Huddinge, Sweden.
authors.forename: Måns
authors.initials: M
authors.lastname: Ullberg
authors.affiliation: Department of Clinical Microbiology, Karolinska University Hospital, Huddinge, Sweden.
authors.forename: Volkan
authors.initials: V
authors.lastname: Özenci
authors.affiliation: Research group for Host-Microbe Interactions, Faculty of Health Sciences, University of Tromsø - 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.
authors.forename: Arnfinn
authors.initials: A
authors.lastname: Sundsfjord
authors.affiliation: Research group for Host-Microbe Interactions, Faculty of Health Sciences, University of Tromsø - 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.
authors.forename: Kristin
authors.initials: K
authors.lastname: Hegstad
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics*; D004196:Disease Outbreaks; D016984:Enterococcus faecium / Q000235:genetics* / Q000302:isolation & purification / Q000472:pathogenicity; D016908:Gram-Positive Bacterial Infections / Q000453:epidemiology* / Q000382:microbiology; D008826:Microbial Sensitivity Tests; D017422:Sequence Analysis, DNA; D013548:Sweden / Q000453:epidemiology; D020713:Vancomycin Resistance / Q000235:genetics; D014774:Virulence / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; C079913:VanB protein, Enterococcus