Listeria monocytogenes in the smoked salmon industry

Smoked salmon is sporadically contaminated with Listerial monocytogenes. Contamination levels are normally low and consumers are probably seldom exposed to risk concentrations. No clones of L. monocytogenes seem to be specific to smoked salmon, some clones found in smoked salmon having been isolated from several sources, including patients. Cold-smoking has been shown to eliminate L. monocytogenes in challenge tests at temperatures from 17.1 to 21.1 degrees C, while from 22.2 to 30 degrees C the bacteria survived. Under natural cold-smoking conditions (19 to 22 degrees C) the frequency and level of L. monocytogenes seems to decrease. Hot-smoking seems to eliminate the bacteria when smoke is applied during the whole heating process. The prevention of recontamination of both cold-smoked and hot-smoked salmon is therefore of great importance. L. monocytogenes multiply considerably in smoked salmon during storage. Growth is faster in challenge tests than in naturally-contaminated smoked salmon. The declared shelf-life under refrigeration should be shorter than that customarily stipulated by many producers. While the sources of L. monocytogenes in smoked salmon processing plants have still to be determined, raw salmon does not seem to be an important source. The main issue for producers is to prevent colonization of the processing environment and spread of the bacteria to products. This should be achieved by the systemic implementation of hygienic measures, including the HACCP approach.