Phage Biology

P. D. Varey 1, 2, T. S. Edrington1*, R. E. Droleskey, R. C. Anderson1, R. O. Elder1, E. Kutter2, A. Brabban2, T. R. Callaway1 and D. J. Nisbet1
* corresponding author

1Food and Feed Safety Research Unit, Agricultural Research Service/USDA, College Station, TX
77845 2The Evergreen State College, Olympia, WA 98505

Escherichia coli O157:H7 is a food-borne human pathogen found in ruminant animals that is of significant concern to the cattle industry. Contamination with O157:H7 has caused the condemnation of large lots of ground beef as well. Widespread efforts are being made to reduce these bacteria in the animals prior to harvest to significantly reduce carcass and groundwater contamination.

Bacteriophages are viruses that specifically infect bacteria and can cause bacterial lysis. Because of their high degree of specificity it has been repeatedly suggested that phage be used to control populations of food borne pathogenic bacteria in animals prior to harvest, but finding the optimal phage for this purpose is complex. When sheep (n=20) from one particular source farm were challenged with an oral gavage of E. coli O157:H7 (ATCC strains 43895 and 700728, which have previously always effectively colonized the gastrointestinal tract of test sheep), the populations of inoculated E. coli O157:H7 decreased rapidly. These resistant sheep were screened for the presence of naturally occurring bacteriophages. Phages were indeed isolated from the feces of these sheep that propagated efficiently in the laboratory in E. coli O157:H7 and were able to infect 17 of 19 different strains of E. coli O157:H7 tested in vitro. Electron microscopy showed that the isolated phage, which we have named ECVS-1, has a T-even morphotype.

Addition of these phage to in vitro ruminal fermentations reduced E. coli O157:H7 populations by 4 logs. (P<0.05). Further in vivo studies are needed to examine the efficacy of treatment with purified phage in reducing populations of E. coli O157:H7 in ruminant animals and the conditions needed to help them become stably carried in such animals for preventive purposes.

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