Biocontrol of Escherichia coli O157 with O157-specific bacteriophages

Escherichia coli O157 antigen-specific bacteriophages were isolated and tes ted to determine their ability to lyse laboratory cultures of Escherichia c oli O157:H7. A total of 53 bovine or ovine fecal samples were enriched for phage, and 5 of these samples were found to contain lytic phages that grow on E. coli O157:H7. Three bacteriophages, designated KH1, KH4, and KH5, wer e evaluated. At 37 or 4 degrees C, a mixture of these three O157-specific p hages lysed all of the E. coli O157 cultures tested and none of the non-O15 7 E. coli or non-E. coli cultures tested. These results required culture ae ration and a high multiplicity of infection. Without aeration, complete lys is of the bacterial cells occurred only after 5 days of incubation and only at 4 degrees C. Phage infection and plaque formation were influenced by th e nature of the host cell O157 lipopolysaccharide (LPS). Strains that did n ot express the O157 antigen or expressed a truncated LPS were not susceptib le to plaque formation or lysis by phage. In addition, strains that express ed abundant mid-range-molecular-weight LPS did not support plaque formation but were lysed in liquid culture. Virulent O157 antigen-specific phages co uld play a role in biocontrol of E. coli O157:H7 in animals and fresh foods without compromising the viability of other normal flora or food quality.