Submitted to: Letters in Applied Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/11/2009
Publication Date: 12/1/2009
Publication URL: http://www.ars.usda.gov/SP2UserFiles/Place/53102000/pdf_pubs/P2308.pdf
Citation: Ibekwe, A.M., Grieve, C.M., Papiernik, S.K., Yang, C.H. 2009. Persistence of Escherichia coli 0157:H7 on the Rhizosphere and Phyllosphere of lettuce. Letters in Applied Microbiology. 49:784-790. Interpretive Summary: Contamination of the environment by pathogenic bacteria is usually done by low populations of the pathogen. Therefore, suppression of human pathogens in agricultural soils and the subsequent prevention of spread into the food chain by contamination of produce must be realized by the adoption of best management practices. This will prevent contamination of preharvest fresh produce and achieve the delivery of microbiological safe produce to consumers. This study was conducted to determine the effects of low levels of soil contamination by E. coli O157:H7 and the subsequent transfer of this pathogen to the edible portion of the plants. E. coli O157:H7 survived on leaf surfaces from 7 days to about 50 days depending on the detection method. However, no pathogen was detected in the inner tissues of the plants. The presence of E. coli O157:H7 on leaf surfaces from contaminated soil continues to be a serious food safety concern and shows that preharvest environments must be properly managed by leafy green vegetable growers to reduce contamination.
Technical Abstract: The major objective of this study was to determine the effects of low levels of E. 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. 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 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 seven days after planting in comparison to 21 days in the rhizosphere. However, real time PCR continued to detect stx1, stx2, and the eae genes throughout the experimental period. E. 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. 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.