Isolation and characterization of five Erwinia amylovora bacteriophages and assessment of phage resistance in strains of Erwinia amylovora

Phages able to infect the fire blight pathogen Erwinia amylovora were isolated from apple, pear, and raspberry tissues and from soil samples collected at sites displaying fire blight symptoms. Among a collection of 50 phage isolates, 5 distinct phages, including relatives of the previously described phages phi Ea1 and phi Ea7 and 3 novel phages named phi Ea100, phi Ea125, and phi Ea116C, were identified based on differences in genome size and restriction fragment pattern. phi Ea1, the phage distributed most widely, had an approximately 46-kb genome which exhibited some restriction site variability between isolates. Phages phi Ea100, phi Ea7, and phi Ea125 each had genomes of approximately 35 kb and could be distinguished by their EcoRI restriction fragment patterns. phi Ea116C contained an approximately 75-kb genome. phi Ea1, phi Ea7, phi Ea100, phi Ea125, and phi Ea116C were able to infect 39, 36, 16, 20, and 40, respectively, of 40 E. amylovora strains isolated from apple orchards in Michigan and 8, 12, 10, 10, and 12, respectively, of 12 E, amylovora strains isolated horn raspberry fields (Rubus spp,) in Michigan. Only 22 of 52 strains were sensitive to all five phages, and 23 strains exhibited resistance to more than one phage, phi Ea116C was more effective than the other phages at lysing E. amylovora strain Ea110 in liquid culture, reducing the final titer of Ea110 by >95% when added at a ratio of 1 PFU per 10 CFU and by 58 to 90% at 1 PFU per 10(5) CFU.