Persistence of Escherichia coli O157:H7 on the rhizosphere and phyllosphere of lettuce.

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 x 10(3) CFU g(-1) of starting DNA in rhizosphere and phyllosphere samples and about 10(2) 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.