A new Danish Listeria monocytogenes phage typing system

A phage typing system was developed for Listeria monocytogenes. Phages were released from clinical and from food strains of L. monocytogenes by mitomycin C induction. The system consists of two subsystems, one of which is used to type L. monocytogenes serotype 1 strains, containing 12 phages, and a second which is used to type serotype 4 strains, containing 14 other phages. For the serotype 1 subsystem, the reproducibility was > or = 90%, the typability 92%, and the discriminatory power, as judged by the discriminatory index, 80%. The corresponding figures for the serotype 4 subsystem were: reproducibility > or = 94%, typability 87%, and discriminatory index 87%. The performance of the whole typing system is sufficient for it to be used for screening purposes.