WHO STUDY ON SUBTYPING LISTERIA-MONOCYTOGENES - RESULTS OF PHAGE-TYPING

A multi-centered study on phage typing of Listeria monocytogenes was c arried out using 80 cultures sent under code and tested in six differe nt laboratories. Phage typing was performed using an international pha ge set in five laboratories and phage sets unique to two laboratories. Testing of cultures sent in duplicate showed similar levels of reprod ucibility to that previously reported. Analysis of results from groups of epidemiologically related cultures showed a high level of agreemen t in all laboratories. Patterns of phage susceptibility were relativel y stable on retesting strains in the same laboratory after long period s of time. However, there was limited comparability between results ob tained from testing the same cultures using the same phages in differe nt laboratories. It is recommended that the phages in the internationa l set be reviewed, and that better inter-laboratory reproducibility ma y be achieved by standardisation of phage suspensions, propagation str ains and methodology, together with the use of centrally propagated ph ages.