Characterization of Listeria monocytogenes isolated from production lines of fresh and cold-smoked fish

Aims: The aims of this study were to characterize strains of Listeria monoc ytogenes isolated from cold-smoking fish plants to establish possible route s of contamination through the processing chain. Methods and Results: Listeria monocytogenes from fresh fish suppliers, raw materials, factory sites and finished products isolated in Portugal (162 is olates) and England (28 isolates) were characterized by serotyping, phage t yping, tetracycline, cadmium and arsenic resistance, and plasmid profiling. On the basis of serotyping and phage typing, the isolates were categorized into eight groups. Although cultures within some of the groups could be fu rther differentiated on the basis of plasmid profiling and cadmium and arse nite typing, consideration of all typing data predominantly clustered toget her isolates from a single location. L. monocytogenes strains: from fresh s almon suppliers were not found in the processing lines; from fresh salmon f rom different locations differed; and from the water where salmon trout wer e farmed differed from those isolated from the fish samples. Significance and Impact of the Study: No clear source or route of contamina tion in the cold-smoked processing chain could be established; however, the se results highlight the complexity in tracking this bacterium through food chains.