title: Protozoan Predation of Escherichia coli O157:H7 Is Unaffected by the Carriage of Shiga Toxin-Encoding Bacteriophages.
abstract: Escherichia coli O157:H7 is a food-borne bacterium that causes hemorrhagic diarrhea and hemolytic uremic syndrome in humans. While cattle are a known source of E. coli O157:H7 exposure resulting in human infection, environmental reservoirs may also be important sources of infection for both cattle and humans. Bacteriophage-encoded Shiga toxins (Stx) carried by E. coli O157:H7 may provide a selective advantage for survival of these bacteria in the environment, possibly through their toxic effects on grazing protozoa. To determine Stx effects on protozoan grazing, we co-cultured Paramecium caudatum, a common ciliate protozoon in cattle water sources, with multiple strains of Shiga-toxigenic E. coli O157:H7 and non-Shiga toxigenic cattle commensal E. coli. Over three days at ambient laboratory temperature, P. caudatum consistently reduced both E. coli O157:H7 and non-Shiga toxigenic E. coli populations by 1-3 log cfu. Furthermore, a wild-type strain of Shiga-toxigenic E. coli O157:H7 (EDL933) and isogenic mutants lacking the A subunit of Stx 2a, the entire Stx 2a-encoding bacteriophage, and/or the entire Stx 1-encoding bacteriophage were grazed with similar efficacy by both P. caudatum and Tetrahymena pyriformis (another ciliate protozoon). Therefore, our data provided no evidence of a protective effect of either Stx or the products of other bacteriophage genes on protozoan predation of E. coli. Further research is necessary to determine if the grazing activity of naturally-occurring protozoa in cattle water troughs can serve to decrease cattle exposure to E. coli O157:H7 and other Shiga-toxigenic E. coli.
authors.affiliation: Department of Veterinary Microbiology and Pathology, College of Veterinary Medicine, Washington State University, Pullman, Washington, United States of America.
authors.forename: Carrie E
authors.initials: CE
authors.lastname: Schmidt
authors.affiliation: Department of Veterinary Microbiology and Pathology, College of Veterinary Medicine, Washington State University, Pullman, Washington, United States of America.
authors.forename: Smriti
authors.initials: S
authors.lastname: Shringi
authors.affiliation: Department of Veterinary Microbiology and Pathology, College of Veterinary Medicine, Washington State University, Pullman, Washington, United States of America.
authors.forename: Thomas E
authors.initials: TE
authors.lastname: Besser
mesh_terms: D000822:Animal Husbandry; D000818:Animals; D061046:Biological Control Agents; D002417:Cattle; D003090:Coliphages / Q000235:genetics; D015169:Colony Count, Microbial; D060766:Drinking Water / Q000382:microbiology; D019453:Escherichia coli O157 / Q000254:growth & development / Q000472:pathogenicity / Q000821:virology*; D020387:Food Chain; D015870:Gene Expression; D006801:Humans; D048488:Paramecium caudatum / Q000502:physiology*; D022622:Shiga Toxin 1 / Q000096:biosynthesis* / Q000235:genetics; D022641:Shiga Toxin 2 / Q000096:biosynthesis* / Q000235:genetics; D013769:Tetrahymena pyriformis / Q000502:physiology*; D014871:Water Microbiology
chemical_list: D061046:Biological Control Agents; D060766:Drinking Water; D022622:Shiga Toxin 1; D022641:Shiga Toxin 2
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