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Keywords:

  • Escherichia coli O157:H7;
  • lettuce;
  • persistence;
  • phyllosphere;
  • real-time PCR;
  • rhizosphere

Abstract

Aims:  The major objective of this study was to determine the effects of low levels of Escherichia coli O157:H7 contamination on plant by monitoring the survival of the pathogen on the rhizosphere and leaf surfaces of lettuce during the growth process.

Methods and Results:  Real-time PCR and plate counts were used to quantify the survival of E. coli O157:H7 in the rhizosphere and leaf surfaces after planting. Real-time PCR assays were designed to amplify the stx1, stx2 and the eae genes of E. coli O157:H7. The detection limit for E. coli O157:H7 quantification by real-time PCR was 2·4 × 103 CFU g−1 of starting DNA in rhizosphere and phyllosphere samples and about 102 CFU g−1 by plate count. The time for pathogens to reach detection limits on the leaf surface by plate counts was 7 days after planting in comparison with 21 days in the rhizosphere. However, real-time PCR continued to detect stx1, stx2 and the eae genes throughout the experimental period.

Conclusion: Escherichia coli O157:H7 survived throughout the growth period as was determined by real-time PCR and by subsequent enrichment and immunomagnetic separation of edible part of plants.

Significance and impact of the Study:  The potential presence of human pathogens in vegetables grown in soils contaminated with E. coli O157:H7 is a serious problem to our national food supply as the pathogen may survive on the leaf surface as they come in contact with contaminated soil during germination.