TYPING LISTERIA-MONOCYTOGENES ISOLATES FROM FISH PRODUCTS AND HUMAN LISTERIOSIS CASES

Seventy-two Listeria monocytogenes isolates originating from 10 differ ent fish products of 12 producers and 47 isolates from human listerios is cases were typed by serotyping and multilocus enzyme electrophoresi s. Seventy-five of these isolates were further subtyped by restriction analysis of genomic DNA with the enzyme XhoI and by pulsed-field gel electrophoresis using the enzymes ApaI and SmaI, The results show that several L. monocytogenes clones identified by multilocus enzyme elect rophoresis are frequently found in fish products of different origins. One of these clones is the same as another previously shown to be fre quently associated with meat and meat products. The epidemic-associate d electrophoretic type 1 was only rarely found in fish products. No as sociation was found between any type of fish product and a particular lineage of L. monocytogenes. Both long-term persistence of a strain an d simultaneous presence of several clearly distinct strains in the pro ducts of single producers were observed. The comparison of L. monocyto genes isolates from human clinical listeriosis cases in Switzerland an d those from imported fish products by use of multilocus enzyme electr ophoresis showed that they do not form two clearly distinct lineages b ut nevertheless belong to two separate populations. None of the 48 sub types distinguished by the combination of all four typing methods coul d be found in both populations of human origin and those of fish origi n.