Phage Biology

Oot, R.1, Perigo S.1, Odegaard, K.1, Wendelsdorf, K.1, Hoyle, N.1, Dutta, G.1, Goldschmidt, L.1, Dyen, M.1, Callaway, T,3 Raya R.1,2, Kutter, E.1, and A. Brabban1.

1 Evergreen State College, Olympia, Washington, 2 Cerela, Tucuman, Argentina, 3 USDA Agricultural Station, College Station, Texas

Escherichia coli O157:H7 is one of the leading public health concerns in America today: human illness has been correlated to water, fresh fruit, vegetables, and undercooked meats that have been contaminated with bovine fecal matter.

Ruminants are the major reservoir that leads to human exposure, with one quarter of U.S. cattle having been shown to shed O157:H7. Virulent bacteriophages are a plausible alternative to antibiotics as a management strategy for controlling the population of E. coli O157:H7 in ruminants and fresh foods, without compromising food quality or disrupting the beneficial normal microbiota of the gut. Virulent bacteriophages active on E. coli O157:H7 were isolated from sheep. Phages CEV1 and CEV2 were isolated from two different flocks of sheep in Texas; a flock that was resistant to E. coli O157:H7 gut colonization and a flock where phage were found in half the population, respectively.

CEV3 and additional phages that infect O157:H7 have been isolated from a local sheep flock in Washington State. CEV1 and CEV3 are T4-like myoviridae, and CEV2 is a siphovirus. CEV1 has been shown in vitro (gut-simulatory chemostat) and in vivo (live animal trial) to eradicate or markedly reduce E. coli O157:H7. Our current research goal is to create a cocktail of phages that will efficiently control E. coli O157:H7 under normal farming practices.

In designing these phage cocktails, it would be ideal to use phages that have different receptors to prevent problems associated with resistance development. The isolation of mutant phages that are active against resistant derivatives of originally sensitive bacteria was carried out using a non-pathogenic strain of O157:H7. Mutants of strain E. coli O157:H7 NCTC 12900 (ATCC 700728) against CEV1, CEV2, and CEV3 have been isolated. Mutant K12900 is sensitive to CEV1, but resistant to CEV2 and CEV3. Mutant R12900 is sensitive to CEV2 and CEV3, but resistant to CEV1. This leads us to believe that CEV1 recognizes a different receptor than CEV2 and CEV3, which may recognize the same receptor. The nature of the receptors has not yet been characterized.

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Last Updated: May 29, 2008

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