[Isolation of Listeria seeligeri and L. welshimeri bacteriophages. Lysotyping of L. monocytogenes, L. ivanovii, L. innocua, L. seeligeri and L. welshimeri].

Recent taxonomic reexamination of Listeria monocytogenes strains as defined in the 8th edition of Bergey's Manual of Determinative Bacteriology allowed to distinguish 5 species among these strains: L. monocytogenes, L. innocua, L. ivanovii, L. welshimeri, and L. seeligeri. As till now only the behaviour of the species L. monocytogenes, L. innocua, and L. ivanovii towards bacteriophages was characterized, the present study aimed at the search for phages occurring on these two new species and to determine their lytic activities towards representative strains of the whole genus. Seven different bacteriophages were isolated from the culture filtrates of 45 strains of L. seeligeri, whereas only one phage was obtained from the filtrates of 17 strains of L. welshimeri. No phage was isolated from the filtrates of L. grayi and L. murrayi strains with our methods. The phage preparations proved stable over a period of 6 to 12 months with titers ranging from 7 X 10(8) to 5 X 10(10). By use of a set of lytic phages which contained in addition to the eight new phages from L. welshimeri and L. seeligeri 23 known phages from L. monocytogenes, L. innocua, and L. ivanovii, 511 selected strains, originating from various sources, especially environment (125 strains), and belonging to all species of Listeria, were studied. 345 (68%) of the 511 strains could be assigned to a lysovar by means of the extended set. The eight new phages showed genus- and serogroup specificity but did not present species-specific reactions. The strains of L. grayi and L. murrayi were untypable using these 31 phages. No relationship between lysovar and serovar on the one side and host and geographic source on the other side was apparent.