OPTIMIZATION OF THE DETECTION OF BACTERIOPHAGES INDUCED FROM LISTERIASP

It is necessary to isolate new phages in order to improve the rate of typeability of Listeria monocytogenes strains. We propose a method whi ch increases the detection of induced phages in the presence of inhibi tory substances synthesized or liberated by the cells during phage pro duction. Of the 29 phages isolated, 11 (38%) were detected by the spot -on-the-lawn technique and 18 (62%) were revealed by the soft-agar tec hnique. To increase the rate of phage detection, both techniques appea r useful. Listeria cultures were subjected to phage typing procedures utilizing these newly isolated phages and the French International set of phages. It appears that the newly isolated phages are good tools f or the differentiation of Listeria strains. Among them, one phage seem s to be complementary to the French International set.