Shiga toxin-producing Escherichia coli (STEC) and atypical enteropathogenic E. coli (aEPEC) in Swedish retail wheat flour

  1. Robert Söderlund
  2. Catarina Flink
  3. Anna Aspán
  4. Erik Eriksson

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Abstract

Wheat flour has been identified as the source of multiple outbreaks of gastrointestinal disease caused by shiga toxin-producing Escherichia coli (STEC). We have investigated the presence and genomic characteristics of STEC and related atypical enteropathogenic E. coli (aEPEC) in 200 bags of Swedish-produced retail wheat flour, representing 87 products and 25 brands. Samples were enriched in modified tryptone soya broth (mTSB) and screened with real-time PCR targeting stx 1 , stx 2 and eae , and the serogroups O157, O121 and O26. Isolation was performed by immunomagnetic separation (IMS) for suspected STEC/aEPEC O157, O121 and O26, and by screening pools of colonies for other STEC. Real-time PCR after enrichment revealed 12 % of samples to be positive for shiga toxin genes ( stx 1 and/or stx 2 ) and 11 % to be positive for intimin ( eae ). Organic production, small-scale production or whole grain did not significantly influence shiga toxin gene presence or absence in a generalized linear mixed model analysis. Eight isolates of STEC were recovered, all of which were intimin-negative. Multiple serotype/sequence type/shiga toxin subtype combinations that have also been found in flour samples in other European countries were recovered. Most STEC types recovered were associated with sporadic cases of STEC among humans in Sweden, but no types known to have caused outbreaks or severe cases of disease (i.e. haemolytic uraemic syndrome) were found. The most common finding was O187:H28 ST200 with stx 2g , with possible links to cervid hosts. Wildlife associated with crop damage is a plausible explanation for at least some of the surprisingly high frequency of STEC in wheat flour.

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  1. Version published to 10.1099/acmi.0.000577.v3 on Access Microbiology
  2. Access Microbiology

    The authors have addressed the reviewers concerns well and this article will be a valuable addition to the literature. We can see the sequence data in ENA and importantly, you would need to ensure the datasets have been released and made publicly available.

  3. Version published to 10.1099/acmi.0.000577.v2 on Access Microbiology
  4. Access Microbiology

    The work presented is clear and the arguments well formed. This study would be a valuable contribution to the existing literature. This is a study that would be of interest to the field and community. The reviewers have highlighted minor concerns with the work presented. Please ensure that you address their comments.

  5. Access Microbiology

    Comments to Author

    The study is well presented and there is a need of collecting data covering this sector and aspects of the food chain. There are two points that should be addressed: 1. Genomic consideration on the isolates. It would be useful to see the genetic relation of the isolates, using a phylogenetic tree and potentially compared the genomes with other publicly available assemblies with same origin. 2. Discussion. Is there any potential risks associated with the presence of STEC or other pathogenic E.coli in this matrices?

    Please rate the manuscript for methodological rigour

    Very good

    Please rate the quality of the presentation and structure of the manuscript

    Very good

    To what extent are the conclusions supported by the data?

    Strongly support

    Do you have any concerns of possible image manipulation, plagiarism or any other unethical practices?

    No

    Is there a potential financial or other conflict of interest between yourself and the author(s)?

    No

    If this manuscript involves human and/or animal work, have the subjects been treated in an ethical manner and the authors complied with the appropriate guidelines?

    Yes

  6. Access Microbiology

    Comments to Author

    1. methods are adequate (please correct line 126, probably "phosphate" missing after "dipotassium hydrogen"), sampling scheme meaningful, data complete and relevant 2. results are well presented and text is easily understood. 3. paper is well organizted, well written in excellent English. Line 171: it would be interesting to give percentages of "eae only" and "stx only" as well as "both stx and eae" positive PCR. Interesting association between deer and O187:H28. 4. the literature cited is relevant and contains all papers pertinent to the subject. The Discussion might be shortened a bit, highlighting the novel aspects of the findings - the highlights are: frequency of STEC in flour, the animal-associated STEC types, the diversity of virulence patterns, and the sparsity of eae plus stx positive isolates, possibly explaining the limited impact on consumer health so far 5. none

    Please rate the manuscript for methodological rigour

    Very good

    Please rate the quality of the presentation and structure of the manuscript

    Very good

    To what extent are the conclusions supported by the data?

    Strongly support

    Do you have any concerns of possible image manipulation, plagiarism or any other unethical practices?

    No

    Is there a potential financial or other conflict of interest between yourself and the author(s)?

    No

    If this manuscript involves human and/or animal work, have the subjects been treated in an ethical manner and the authors complied with the appropriate guidelines?

    Yes

  7. Version published to 10.1099/acmi.0.000577.v1 on Access Microbiology