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Type III effector genes and other virulence factors of Shiga toxin-encoding Escherichia coli isolated from wastewater

Authors

  • Alexandre Martínez-Castillo,

    1. Department of Microbiology, University of Barcelona, Diagonal 643, Annex, Floor 0, 08028 Barcelona, Spain.
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  • Anna Allué-Guardia,

    1. Department of Microbiology, University of Barcelona, Diagonal 643, Annex, Floor 0, 08028 Barcelona, Spain.
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  • Ghizlane Dahbi,

    1. Laboratorio de Referencia de E. coli (LREC), Department of Microbiology and Parasitology, Faculty of Veterinary Science, University of Santiago de Compostela, 27002 Lugo, Spain.
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  • Jorge Blanco,

    1. Laboratorio de Referencia de E. coli (LREC), Department of Microbiology and Parasitology, Faculty of Veterinary Science, University of Santiago de Compostela, 27002 Lugo, Spain.
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  • Kristina Creuzburg,

    1. Institute of Food Science and Biotechnology, Department of Food Microbiology, University of Hohenheim, Garbenstrasse 28, 70599 Stuttgart, Germany.
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  • Herbert Schmidt,

    1. Institute of Food Science and Biotechnology, Department of Food Microbiology, University of Hohenheim, Garbenstrasse 28, 70599 Stuttgart, Germany.
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  • Maite Muniesa

    Corresponding author
    1. Department of Microbiology, University of Barcelona, Diagonal 643, Annex, Floor 0, 08028 Barcelona, Spain.
      E-mail mmuniesa@ub.edu; Tel. (+34) 93 4039386; Fax (+34) 93 4039047.
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E-mail mmuniesa@ub.edu; Tel. (+34) 93 4039386; Fax (+34) 93 4039047.

Summary

Pathogenic Shiga toxin-producing Escherichia coli (STEC) strains share the genes encoding Shiga toxins (stx) and many other virulence factors. The classification and evolutionary studies of pathogenic E. coli based on their virulence genes have been conducted with E. coli isolated from human and animal infections or outbreaks. In this study, we used 103 STEC strains isolated from faecally polluted water environments to analyse 23 virulence genes (stx1, cdt, hlyA, saa, eae, three type III effector genes encoded within the locus of enterocyte effacement (LEE) and 15 non-LEE-encoded type III effector genes). Despite the presence of several stx2 variants, our isolates demonstrated low prevalence of the virulence genes (only 46.6% of the strains were positive for virulence determinants). Among these, the largest repertoire was found in a few O157:H7 isolates (most from cattle wastewater and one from sewage), while other serotypes showed fewer virulence determinants. The occurrence of most virulence genes seemed to be independent from one another. This was clear for hlyA (the most prevalent), cdt and cif (the least prevalent). Other effector genes, could be found or not in combination with others, suggesting that they can be mobilized independently. Our data suggest that E. coli strains can evolve separately by independently acquiring mobile genetic elements.

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