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- Characterization of Listeria monocytogenes isolated from production lines of fresh and cold-smoked fishPublication . Vaz-Velho, M.; Duarte, G.; McLauchlin, J.; Gibbs, P.Aims: The aims of this study were to characterize strains of Listeria monocytogenes isolated from cold-smoking fish plants to establish possible routes 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 isolates) and England (28 isolates) were characterized by serotyping, phage typing, 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 further differentiated on the basis of plasmid profiling and cadmium and arsenite typing, consideration of all typing data predominantly clustered together isolates from a single location. L. monocytogenes strains: from fresh salmon suppliers were not found in the processing lines; from fresh salmon from different locations differed; and from the water where salmon trout were farmed differed from those isolated from the fish samples. Significance and Impact of the Study: No clear source or route of contamination in the cold-smoked processing chain could be established; however, these results highlight the complexity in tracking this bacterium through food chains.
- Note. Occurrence of Listeria spp. in salmon-trout (Onchorhyncus mykiss) and salmon (Salmo salar)Publication . Vaz-Velho, M.; Duarte, G.; Gibbs, P.Salmon-trout (Onchorhyncus mykiss) and salmon (Salmo salar) are the main raw materiaIs in the cold-smoked fish industry. It is important to prevent the contamination of these ready-to-eat products with Listeria monocytogenes and other (Listeria spp.) because the temperature used in the cold-smoking process is not sufficient to inactivate these organisms. The presence of Listeria spp. and L. monocytogenes in the cold-smoked salmon and salmon-trout processing chains of three Portuguese factories examined was already confirmed in previous studies. Thus, it was important to ascertain the possible sources of contamination, the raw material being the most important one. AlI the Portuguese cold-smoking fish factories use fresh salmon-trout from two trout farms in the north of Portugal and Norwegian salmon which arrives by lorry every week under refrigeration, imported always by the same company; 88 samples of salmon and salmon-trout were analysed; 67 environrnental samples from the two trout farms were also examined. The overalI frequency (n =40) of Listeria spp. and L. monocytogenes in salmon was 12 and 0% respectively. The overalI frequency (n =48) of Listeria spp. and L. monocytogenes in salmon-trout was 6.3 and 2.1% respectively. Listeria was not found in the environmental samples.