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    Tracing back multidrug-resistant bacteria in fresh herb production: from chive to source through the irrigation water chain

    Gekenidis, Maria-Theresia and Schöner, Ulrich and von Ah, Ueli and Schmelcher, Mathias and Walsh, Fiona and Drissner, D. (2018) Tracing back multidrug-resistant bacteria in fresh herb production: from chive to source through the irrigation water chain. FEMS Microbiology Ecology, 94 (11). fiy149. ISSN 1574-6941

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    Environmental antibiotic-resistant bacteria (ARB) can be transferred to humans through foods. Fresh produce in particular is an ideal vector due to frequent raw consumption. A major contamination source of fresh produce is irrigation water. We hypothesized that water quality significantly affects loads of ARB and their diversity on fresh produce despite various other contamination sources present under agricultural practice conditions. Chive irrigated from an open-top reservoir or sterile-filtered water (control) was examined. Heterotrophic plate counts (HPC) and ARB were determined for water and chive with emphasis on Escherichia coli and Enterococcus spp. High HPC of freshly planted chive decreased over time and were significantly lower on control- vs. reservoir-irrigated chive at harvest (1.3 log (CFU/g) lower). Ciprofloxacin- and ceftazidime-resistant bacteria were significantly lower on control-irrigated chive at harvest and end of shelf life (up to 1.8 log (CFU/g) lower). Escherichia coli and Enterococcus spp. repeatedly isolated from water and chive proved resistant to up to six or four antibiotic classes (80% or 49% multidrug-resistant, respectively). Microbial source tracking identified E. coli-ST1056 along the irrigation chain and on chive. Whole-genome sequencing revealed that E. coli-ST1056 from both environments were clonal and carried the same transmissible multidrug-resistance plasmid, proving water as source of chive contamination. These findings emphasize the urgent need for guidelines concerning ARB in irrigation water and development of affordable water disinfection technologies to diminish ARB on irrigated produce.

    Item Type: Article
    Additional Information: © FEMS 2018. This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs licence (, which permits non-commercial reproduction and distribution of the work, in any medium, provided the original work is not altered or transformed in any way, and that the work is properly cited. For commercial re-use, please contact
    Keywords: irrigation water; fresh produce; antibiotic resistance; E. coli; Enterococcus spp; microbial source tracking;
    Academic Unit: Faculty of Science and Engineering > Biology
    Item ID: 10779
    Identification Number:
    Depositing User: Fiona Walsh
    Date Deposited: 15 May 2019 10:55
    Journal or Publication Title: FEMS Microbiology Ecology
    Publisher: Oxford University Press
    Refereed: Yes
    Use Licence: This item is available under a Creative Commons Attribution Non Commercial Share Alike Licence (CC BY-NC-SA). Details of this licence are available here

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