title: Impact of microbial diversity on rapid detection of enterohemorrhagic Escherichia coli in surface waters.
abstract: Enterohemorrhagic Escherichia coli (EHEC) are a physiologically, immunologically and genetically diverse collection of strains that pose a serious water-borne threat to human health. Consequently, immunological and PCR assays have been developed for the rapid, sensitive detection of presumptive EHEC. However, the ability of these assays to consistently detect presumptive EHEC while excluding closely related non-EHEC strains has not been documented. We conducted a 30-month monitoring study of a major metropolitan watershed. Surface water samples were analyzed using an immunological assay for E. coli O157 (the predominant strain worldwide) and a multiplex PCR assay for the virulence genes stx(1), stx(2) and eae. The mean frequency of water samples positive for the presence of E. coli O157, stx(1) or stx(2) genes, or the eae gene was 50%, 26% and 96%, respectively. Quantitative analysis of selected enriched water samples indicated that even in samples positive for E. coli O157 cells, stx(1)/stx(2) genes, and the eae gene, the concentrations were rarely comparable. Seventeen E. coli O157 strains were isolated, however, none were EHEC. These data indicate the presence of multiple strains similar to EHEC but less pathogenic. These findings have important ramifications for the rapid detection of presumptive EHEC; namely, that current immunological or PCR assays cannot reliably identify water-borne EHEC strains.
authors.affiliation: USDA-Agricultural Research Service, Environmental Microbial Safety Laboratory, Beltsville, MD 20705-2350, USA. sheltond@ba.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: James A
authors.initials: JA
authors.lastname: Higgins
authors.forename: Jo Ann S
authors.initials: JA
authors.lastname: Van Kessel
authors.forename: Michael L
authors.initials: ML
authors.lastname: Perdue
authors.forename: Kenneth T
authors.initials: KT
authors.lastname: Belt
authors.forename: Jonathan
authors.initials: J
authors.lastname: Russell-Anelli
authors.forename: Chitrita
authors.initials: C
authors.lastname: Debroy
mesh_terms: D018829:Adhesins, Bacterial / Q000235:genetics; D019453:Escherichia coli O157 / Q000145:classification / Q000235:genetics / Q000302:isolation & purification*; D029968:Escherichia coli Proteins / Q000235:genetics; D007118:Immunoassay / Q000379:methods*; D016133:Polymerase Chain Reaction / Q000379:methods*; D012703:Serotyping / Q000379:methods; D022622:Shiga Toxin 1 / Q000235:genetics; D022641:Shiga Toxin 2 / Q000235:genetics; D014871:Water Microbiology
chemical_list: D018829:Adhesins, Bacterial; D029968:Escherichia coli Proteins; D022622:Shiga Toxin 1; D022641:Shiga Toxin 2; C073819:eaeA protein, E coli