Isolation and characterization of nine bacteriophages that lyse O149 enterotoxigenic Escherichia coli

The goal of this study was to isolate and characterize phages that might be used in prevention and treatment of porcine post-weaning diarrhea due to O149 enterotoxigenic E. coli (ETEC). Serotype O149:H10:F4 was especially targeted because this is the dominant ETEC serotype. Mixtures of 10 strains of O149:H10:F4 ETEC and of 10 O149:H43:F4 ETEC were used as hosts for isolation of phages in sewage from 38 Ontario pig farms. Six phages (GJ1-GJ6) that lysed O149:H10:F4 ETEC and three (GJ7-GJ9) that lysed O149:H43:F4 ETEC were isolated. All phages produced large, clear plaques. All nine phages had necks and contractile tails and therefore belonged to the Myoviridae. Their estimated genome sizes were 48.3-50.7kb and their restriction enzyme fragments suggested that they were closely related. Phages GJ1-GJ6 lysed 99-100% of 85 O149:H10:F4 ETEC, 0-12% of 42 O149:H43:F4 ETEC, 3-35% of 37 non-O149 porcine ETEC, and 6-68% of the 72 strains of the ECOR collection. Phages GJ7-GJ9 lysed 86-98% of the O149:H43:F4 ETEC, 2-53% of the O149:H10:F4 ETEC, and 24-41% of the non-O149 porcine ETEC. Titres of the nine phages were unaffected by exposure for 16h to pH 5-9. Among phages GJ1-GJ6, resistance of O149:H10:F4 ETEC to one phage was generally not accompanied by resistance to other phages. It is concluded that the nine phages are suitable candidates for prophylaxis and therapy of porcine post-weaning diarrhea due to O149 ETEC.