title: Relationship between eae and stx virulence genes and Escherichia coli in an agricultural watershed: implications for irrigation water standards and leafy green commodities.
abstract: The California Leafy Greens Marketing Agreement (LGMA) was adopted in an effort to minimize the risk of contamination of leafy greens with enteric pathogens from a variety of sources, including ground and surface irrigation waters. The LGMA contains standards similar to those established for recreational waters, based on Escherichia coli concentrations. However, no correlation between E. coli and any specific waterborne pathogen(s) has been reported. We conducted this monitoring study in an agricultural watershed to (i) evaluate spatial and temporal fluctuations in E. coli populations and virulence genes associated with pathogenic E. coli and (ii) investigate whether a relationship could be established between E. coli and virulence genes. The virulence genes targeted for analysis were the eae and stx genes, encoding for intimin and Shiga-like toxins, respectively; they were detected with PCR methods. E. coli concentrations and eae and stx prevalence varied both spatially and temporally. In general, both were higher in agricultural than in forested areas and were higher in the summer and fall seasons than in winter. The eae and stx genes were prevalent throughout the watershed. However, in the absence of actual isolates, no conclusions could be drawn regarding the prevalence of specific pathogenic E. coli. No correlation was observed between E. coli concentrations and virulence genes; lower E. coli concentrations were not necessarily associated with decreased prevalence of eae and stx genes. These results suggest that the LGMA standards might not adequately address the issue of waterborne contamination, and that alternative criteria might be required.
authors.affiliation: U.S. Department of Agriculture, Agricultural Research Service, Environmental Microbial and Food Safety Laboratory, Building 173, Beltsville Agricultural Research Center-East, 10300 Baltimore Avenue, Beltsville, Maryland 20705, USA. dan.shelton@ars.usda.gov
authors.forename: Daniel R
authors.initials: DR
authors.lastname: Shelton
authors.forename: Jeffrey S
authors.initials: JS
authors.lastname: Karns
authors.forename: Cary
authors.initials: C
authors.lastname: Coppock
authors.forename: Jitu
authors.initials: J
authors.lastname: Patel
authors.forename: Manan
authors.initials: M
authors.lastname: Sharma
authors.forename: Yakov A
authors.initials: YA
authors.lastname: Pachepsky
mesh_terms: D018829:Adhesins, Bacterial; D000383:Agriculture / Q000379:methods*; D003257:Consumer Product Safety; D004926:Escherichia coli / Q000472:pathogenicity*; D029968:Escherichia coli Proteins / Q000235:genetics*; D005506:Food Contamination / Q000032:analysis* / Q000517:prevention & control; D005618:Fresh Water / Q000382:microbiology; D006801:Humans; D045483:Rivers / Q000382:microbiology; D012621:Seasons; D022621:Shiga Toxin / Q000235:genetics*; D014675:Vegetables / Q000382:microbiology*; D014774:Virulence / Q000235:genetics
chemical_list: D018829:Adhesins, Bacterial; D029968:Escherichia coli Proteins; C073819:eaeA protein, E coli; D022621:Shiga Toxin