The Incidence of Listeria spp., Salmonella spp., and Clostridium botulinum in Smoked Fish and Shellfish

Abstract

The frequency of occurrence of Listeria spp., Salmonella spp., and Clostridium botulinum is samples of smoked finfish and smoked shellfish was analyzed over a 5-year period. Listeria monocytogenes were isolated from 14% of 1,080 samples. For those samples where the smoke process was known, the incidence of L. monocytogenes was higher in cold-smoked than hot-smoked products (51 of 240 cold-smoked compared to 19 of 215 hot-smoked products). Listeria species other than L. monocytogenes were also detected (in 7.2% of cold-smoked and 3.8% of hot-smoked products). The time and temperature smoke processing guidelines are reviewed for a few state authorities. L. monocytogenes was isolated from 15.2% of the 559 samples of foreign origin. There were four countries for which more than 70 samples were analyzed: Canada, Norway, the Philippines, and the United Kingdom. The occurrence of L. monocytogenes in samples from these four countries was 14.3%, 23.7%, 0%, and 16.1%, respectively. The 521 samples originating in the United States were processed by 194 plants. Thirty-seven plants in 13 states produced contaminated product. Salmonella species were isolated from 5 (3.2%) of 156 samples tested for this organism. All positive samples were of foreign origin (4 from the Philippines and 1 from the United Kingdom). No C. botulinum spores were detected in any of the 201 vacuum-packed samples tested for this organism.

Molecular Studies on the Ecology of Listeria monocytogenes in the Smoked Fish Processing Industry

“…L. monocytogenes was detected in a variety of environmental, raw material, in-process, and cold-smoked fish samples (Table 2) collected from three smoked fish processing plants. We isolated L. monocytogenes from 11.5% of finished product samples, consistent with the prevalence range reported by previous sur- veys (6,21,27). As L. monocytogenes is a common contaminant of the food processing environment (6, 16), we were not surprised that this organism was isolated from over 20% of our environmental samples.…”

Preservation of Fish by Curing

“…Also, no toxin was detected by Cann and Taylor (1979) at 2.5-3.5% NaCl (w/w) in hot-smoked trout stored at 10 • C. In addition, vacuum packaging is one of the effective methods for inhibition of Clostridium botulinum growth. No spores of C. botulinum were detected by Heinitz and Johnson (1998) from 201 vacuum-packed smoked fish and shellfish products. However, 1.7% of positive samples were found in cold-smoked salmon with a level of <1 spore/kg (Nielsen and Pedersen, 1967) and 3% of 64 samples of cold-smoked rainbow trout were positive with levels in the range 40-290 spores/kg .…”

Potential hazards in smoke-flavored fish

“…The variation is high, ranging from 0 to 100% according to various products (Table 2). It seems that the incidence of L. monocytogenes was higher in cold-smoked products (51 of 240) than in hot-smoked products (19 of 215) (Heinitz and Johnson, 1998). Moreover the vacuum-packaging, which ensures long shelf life of the product, is a current issue.…”