Oral Presentation Australian Society for Microbiology Annual Scientific Meeting 2013

Elucidating the molecular mechanisms of Escherichia coli O157:H7 adherence to the roots of fresh produce plants. (#133)

Ashleigh Holmes 1 , Yannick Rossez 1 , Louise Birse 1 , David Gally 2 , Nicola Holden 1
  1. James Hutton Institute, Dundee, United Kingdom
  2. Infection and Immunity Division, The Roslin Institute and R(D)SVS, University of Edinburgh, Edinburgh, United Kingdom

Enterohaemorrhagic Escherichia coli O157:H7 are important food-borne pathogens often associated with consumption of contaminated meat.  However, a significant number of outbreaks have been attributed to the consumption of fresh produce.  There is mounting evidence that plants can act as hosts for E. coli O157:H7 and not just as vectors for transmission, although the mechanisms of colonisation are not yet fully defined.  The aim of this study is to identify bacterial surface-expressed factors that mediate the adherence of E. coli O157:H7 to plant roots.
A bacteria artificial clone (BAC) library, representing the genome of E. coli O157:H7 (Sakai), was screened for adherence to spinach roots and analysed using DNA microarrays.  The BAC library screen enriched for regions including the F9 main structural subunit.  This supports previous transcriptomic data showing that F9 and E. coli common pili (ECP) fimbrial clusters are upregulated in planta.  A BAC clone that encodes the main structural subunit of F9 (ECs2113) was assessed for its adherence to spinach and lettuce roots; individually and in competition with the empty BAC control.
F9 and ECP structural subunit mutants of E. coli O157:H7 strains Sakai and TUV93-0 were tested for adherence to roots in vitro.  E. coli Sakai F9 and ECP mutants display a significant reduction in adherence to spinach roots compared to the isogenic parental strain.  The E. coli TUV93-0 F9 mutant also displayed a significant reduction in adherence to spinach roots compared to wild-type.
E. coli O157:H7 are able to adhere to living plant roots and this interaction is facilitated by the expression of F9 and ECP fimbriae.  Adherence to plant roots is a newly discovered role for these fimbriae, as F9 has been described for adhesion to bovine epithelial cells1 and ECP in adhesion to both mammalian epithelial cells2 and leaf tissue3.

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  3. Saldana Z, Sanchez E, Xicohtencatl-Cortes J, Puente JL, Giron JA: Surface structures involved in plant stomata and leaf colonization by shiga-toxigenic Escherichia coli O157:H7. Front Microbiol 2011, 2:119.