CONTAMINATION PATTERN OF LISTERIA-MONOCYTOGENES AND OTHER LISTERIA SPP IN A SALMON SLAUGHTERHOUSE AND SMOKED SALMON PROCESSING PLANT

A smoked salmon processing plant including a smokehouse and a slaughte rhouse was examined far the occurrence of Listeria monocytogenes and o ther Listeria spp. From a total of 475 samples the overall frequency o f L. monocytogenes was 16%, while other Listeria spp. were found in 22 % of the samples. L. monocytogenes was most often detected in samples from the smokehouse, where 29% of the environmental and 26% of the fis h samples during processing contained the bacteria. 17% of the fish ra w material to the smokehouse were contaminated, while 11% of the sampl es from vacuum-packed smoked salmon were positive for L. monocytogenes . The slaughterhouse was sporadically contaminated, but L. monocytogen es was not found in 50 samples of slaughtered fish. L. monocytogenes w as found in the seawater outside the slaughterhouse. Multilocus enzyme electrophoresis divided the isolated L. monocytogenes strains into 11 electrophoretic types (ETs). One ET, ET-6, which is the most common E T in Norway, seemed to have colonized the smokehouse. Isolates from th e seawater, from the slaughterhouse and from fish coming into the smok ehouse, before filleting, were other ETs.