OCCURRENCE OF LISTERIA SPP. IN SALMON-TROUT (ONCORHYNCHUS-MYKISS) ANDSALMON (SALMO-SALAR)

Salmon-trout (Onchorhyncus mykiss) and salmon (Salmo salar) are the ma in raw materials 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 orga nisms. The presence of Listeria spp. and L. monocytogenes in the cold- smoked salmon and salmon-trout processing chains of three Portuguese f actories 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. All the Portuguese cold-smo king fish factories use fresh salmon-trout from two trout farms in the north of Portugal and Norwegian salmon which arrives by lorry every w eek under refrigeration, imported always by the same company; 88 sampl es of salmon and salmon-trout were analysed; 67 environmental samples from the two trout farms were also examined. The overall frequency (n = 40) of Listeria spp. and L. monocytogenes in salmon was 12 and 0% re spectively. The overall frequency (n = 48) of Listeria spp. and L. mon ocytogenes in salmon-trout was 6.3 and 2.1% respectively. Listeria was not found in the environmental samples.