An Association between Capsulation and Phage Sensitivity in Erwinia amylovora

Abstract

DURING a recent outbreak of fire blight in Britain^1,2 more than 150 isolations of the pathogen, Erwinia amylovora, have been made in this laboratory. On initial plating of infected material two types of colony are often observed³. The dominant type has characteristic markings on ‘Yeastrel’ peptone agar plates incubated at 30° C. For convenience, strains which form this type of colony are called ‘typical’; those forming the second type of colony, which is relatively featureless, and less opaque, are called ‘atypical’. Some strains are intermediate in character, even after re-streaking several times. With some such strains the opacity of individual colonies on a single streak plate may show considerable variation, with others, each individual colony appears mottled; marking may or may not be apparent on the more opaque colonies. Some ‘typical’ strains regularly yield a small proportion of unmarked colonies.