Protozoan Predation of Escherichia coli O157:H7 Is Unaffected by the Carriage of Shiga Toxin-Encoding Bacteriophages

• Published in: PloS one Vol. 11; no. 1; p. e0147270
• Main Authors: Schmidt, Carrie E., Shringi, Smriti, Besser, Thomas E.
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 29.01.2016; Public Library of Science (PLoS)
• Subjects: Animal Husbandry; Animals; Bacteria; Bacteriophages; Biological Control Agents; Biology and Life Sciences; Cattle; Coding; Coliphages - genetics; Colony Count, Microbial; Deoxyribonucleic acid; Diarrhea; DNA; Drinking water; Drinking Water - microbiology; E coli; Ecology and Environmental Sciences; Escherichia coli; Escherichia coli O157 - growth & development; Escherichia coli O157 - pathogenicity; Escherichia coli O157 - virology; Exposure; Food Chain; Gene Expression; Genes; Grazing; Health aspects; Hemolytic uremic syndrome; Hemorrhage; Humans; Infections; Laboratories; Medicine and Health Sciences; Microbiology; Mutants; Paramecium caudatum; Paramecium caudatum - physiology; Pathology; Phages; Physiological aspects; Predation; Predation (Biology); Protozoa; Research and Analysis Methods; Shiga toxin; Shiga Toxin 1 - biosynthesis; Shiga Toxin 1 - genetics; Shiga Toxin 2 - biosynthesis; Shiga Toxin 2 - genetics; Tetrahymena pyriformis; Tetrahymena pyriformis - physiology; Tetrahymena thermophila; Toxicity; Toxins; Troughs; Veterinary colleges; Veterinary medicine; Water Microbiology; Water sources; United States; United States > US
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0147270

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.