SUMMARY: The bacteriophages of have been studied with respect to isolation techniques and their use as diagnostic tools and as aids in epidemiological investigations. The occurrence of lysogeny was investigated in 123 strains isolated from human and animal sources throughout the world. Conventional procedures for isolation of phage were unreliable with Listeria since lysogenic strains did not always, by spontaneous lysis, release a detectable amount of phage. However, after exposure to ultraviolet radiation, such strains were induced to produce up to 10 plaque-forming particles/ml. Some strains which did not release phage produced substances after irradiation possibly analogous to colicines. The lytic spectrum of 11 phages against 149 strains of Listeria was studied and a system of classification, with five of these phages, was used to place 127 of these strains in 8 phage types. Nearly all of the untypable strains were rough, undergoing dissociation, or were lysogenic. Phage susceptibility appeared to be closely associated with the serological type of the strain, but showed no relation to the animal source or the geographical origin. These studies indicated that Listeria phages could be used as a means of generic identification and also as a substitute for or an adjunct to serological typing in epidemiological investigations.


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