Microevolutionary events involving narrow host plasmids influences local fixation of vancomycin-resistance in Enterococcus populations

PLoS One. 2013;8(3):e60589. doi: 10.1371/journal.pone.0060589. Epub 2013 Mar 29.

Abstract

Vancomycin-resistance in enterococci (VRE) is associated with isolates within ST18, ST17, ST78 Enterococcus faecium (Efm) and ST6 Enterococcus faecalis (Efs) human adapted lineages. Despite of its global spread, vancomycin resistance rates in enterococcal populations greatly vary temporally and geographically. Portugal is one of the European countries where Tn1546 (vanA) is consistently found in a variety of environments. A comprehensive multi-hierarchical analysis of VRE isolates (75 Efm and 29 Efs) from Portuguese hospitals and aquatic surroundings (1996-2008) was performed to clarify the local dynamics of VRE. Clonal relatedness was established by PFGE and MLST while plasmid characterization comprised the analysis of known relaxases, rep initiator proteins and toxin-antitoxin systems (TA) by PCR-based typing schemes, RFLP comparison, hybridization and sequencing. Tn1546 variants were characterized by PCR overlapping/sequencing. Intra- and inter-hospital dissemination of Efm ST18, ST132 and ST280 and Efs ST6 clones, carrying rolling-circle (pEFNP1/pRI1) and theta-replicating (pCIZ2-like, Inc18, pHTβ-like, two pRUM-variants, pLG1-like, and pheromone-responsive) plasmids was documented. Tn1546 variants, mostly containing ISEf1 or IS1216, were located on plasmids (30-150 kb) with a high degree of mosaicism and heterogeneous RFLP patterns that seem to have resulted from the interplay between broad host Inc18 plasmids (pIP501, pRE25, pEF1), and narrow host RepA_N plasmids (pRUM, pAD1-like). TAs of Inc18 (ω-ε-ζ) and pRUM (Axe-Txe) plasmids were infrequently detected. Some plasmid chimeras were persistently recovered over years from different clonal lineages. This work represents the first multi-hierarchical analysis of VRE, revealing a frequent recombinatorial diversification of a limited number of interacting clonal backgrounds, plasmids and transposons at local scale. These interactions provide a continuous process of parapatric clonalization driving a full exploration of the local adaptive landscape, which might assure long-term maintenance of resistant clones and eventually fixation of Tn1546 in particular geographic areas.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Anti-Bacterial Agents / pharmacology*
  • DNA Transposable Elements
  • DNA, Bacterial / genetics
  • Enterococcus faecium / drug effects*
  • Enterococcus faecium / genetics
  • Enterococcus faecium / isolation & purification
  • Gram-Positive Bacterial Infections / drug therapy*
  • Gram-Positive Bacterial Infections / epidemiology
  • Humans
  • Molecular Sequence Data
  • Plasmids / genetics
  • Portugal / epidemiology
  • Vancomycin / pharmacology*
  • Vancomycin Resistance*

Substances

  • Anti-Bacterial Agents
  • DNA Transposable Elements
  • DNA, Bacterial
  • Vancomycin

Associated data

  • GENBANK/AAL59457
  • GENBANK/AE016833
  • GENBANK/AF507977
  • GENBANK/AM932524
  • GENBANK/DQ198088
  • RefSeq/NC_002630

Grants and funding

Ana Freitas was supported by a fellowship from Fundação para a Ciência e Tecnologia (SFRH/BD/24604/2005) and from the European Union (LSHE-CT-2007-037410). This work was funded by grants from the European Union (6FPEU-LSHE-CT-2007-037410_ACE and 7FPEU-HEALTH-F3-2011-282004_EvoTAR), the Ministry of Economy and Competitiveness of Spain-Instituto de Salud Carlos III (PS09/02381, PI10/01081, PI12/01581), and Fundação para a Ciência e Tecnologia of Portugal (PTDC/AAC-AMB/103386/2008 and PEst-C/EQB/LA0006/2011). Work in MVFs lab is funded by the the Ministry of Economy and Competitiveness of Spain-Instituto de Salud Carlos III (PI10/01081 and CES08/008) and the Spanish Network for the Research in Infectious Diseases (REIPIRD06/0008/0031). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.