title: Fate of Escherichia coli O157:H7 in irrigation water on soils and plants as validated by culture method and real-time PCR.
abstract: One of the most common vehicles by which Escherichia coli O157:H7 may be introduced into crops is contaminated irrigation water. Water contamination is becoming more common in rural areas of the United States as a result of large animal operations, and up to 40% of tested drinking-water wells are contaminated with E. coli. In this study, 2 contrasting soil samples were inoculated with E. coli O157:H7 expressing green fluorescent protein through irrigation water. Real-time PCR and culture methods were used to quantify the fate of this pathogen in phyllosphere (leaf surface), rhizosphere (volume of soil tightly held by plant roots), and non-rhizosphere soils. A real-time PCR assay was designed with the eae gene of E. coli O157:H7. The probe was incorporated into real-time PCR containing DNA extracted from the phyllosphere, rhizosphere, and non-rhizosphere soils. The detection limit for E. coli O157:H7 quantification by real-time PCR was 1.2 x 10(3) in the rhizosphere, phyllosphere, and non-rhizosphere samples. E. coli O157:H7 concentrations were higher in the rhizosphere than in the non-rhizosphere soils and leaf surfaces, and persisted longer in clay soil. The persistence of E. coli O157:H7 in phyllosphere, rhizosphere, and non-rhizosphere soils over 45 days may play a significant part in the recontamination cycle of produce in the environment. Therefore, the rapidity of the real-time PCR assay may be a useful tool for quantification and monitoring of E. coli O157:H7 in irrigation water and on contaminated fresh produce.
authors.affiliation: USDA-ARS, George E. Brown Jr. Salinity Lab, Riverside, CA 92507, USA. aibekwe@ussl.ars.usda.gov
authors.forename: A Mark
authors.initials: AM
authors.lastname: Ibekwe
authors.forename: Pamela M
authors.initials: PM
authors.lastname: Watt
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Shouse
authors.forename: Catherine M
authors.initials: CM
authors.lastname: Grieve
mesh_terms: D018829:Adhesins, Bacterial / Q000235:genetics; D015169:Colony Count, Microbial / Q000379:methods*; D004269:DNA, Bacterial / Q000032:analysis; D019453:Escherichia coli O157 / Q000302:isolation & purification*; D029968:Escherichia coli Proteins / Q000235:genetics; D005516:Food Microbiology; D018515:Plant Leaves / Q000382:microbiology; D018517:Plant Roots / Q000382:microbiology; D016133:Polymerase Chain Reaction; D012988:Soil Microbiology; D014871:Water Microbiology
chemical_list: D018829:Adhesins, Bacterial; D004269:DNA, Bacterial; D029968:Escherichia coli Proteins; C073819:eaeA protein, E coli