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PLoS One. 2014 Aug 25;9(8):e103274. doi: 10.1371/journal.pone.0103274. eCollection 2014.

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.

Author information

1
Research group for Host-Microbe Interactions, Faculty of Health Sciences, University of Tromsø - The Arctic University of Norway, Tromsø, Norway.
2
Unit for antibiotics and infection control, the Public Health Agency of Sweden, Solna, Sweden.
3
Department of Clinical Microbiology, Karolinska University Hospital, Huddinge, Sweden.
4
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.

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.

PMID:
25153894
PMCID:
PMC4143159
DOI:
10.1371/journal.pone.0103274
[Indexed for MEDLINE]
Free PMC Article
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