INCIDENCE AND SOURCES OF LISTERIA-MONOCYTOGENES IN COLD-SMOKED FISHERY PRODUCTS AND PROCESSING PLANTS

Cold-smoked salmon processing plants were surveyed to determine the oc currence and sources of L. manocytogenes contamination. Sanitation and cleanup procedures adequately eliminated L. monocytogenes from the pr ocessing line and equipment, but recontamination occurred soon after r esumption of processing. The primary source of contamination proved to be the surface areas of frozen or fresh raw fish coming into the plan t. Listeria species were not isolated from the flesh except when they were introduced during the filleting operation, by the injection of re circulated brine, or in localized areas where there were pre-existing bruises. Penetration of L. manocytogenes into intact flesh via the vas cular system did not occur when fresh fish were immobilized with carbo n dioxide and bled, nor when frozen, headed, and eviscerated fish were thawed for 20 h in water inoculated with 44 L. monocytogenes organism s per ml. Populations of L. monocytogenes inoculated onto the surface of brined salmon portions changed very little during a cold-smoke proc ess at 72 to 87 degrees F (22.2 to 30.6 degrees C) for 20 h, with or w ithout applied smoke; but when the processing temperature was lowered to 63 to 70 degrees F (17.2 to 21.1 degrees C), populations decreased 10- to 25-fold when smoke was applied. L. monocytogenes injected into the interior of these portions increased 2- to 6-fold at 63 to 70 degr ees F (17.2 to 21.1 degrees C) and 100-fold at 72 to 87 degrees F (22. 2 to 30.6 degrees C), regardless of the presence of smoke. L. monocyto genes was enumerated in 48 contaminated finished products collected fr om six different processing plants. L. monocytogenes populations range d from 0.3 to 34.3 cells per g, with a mean of 6.2 per g and a median of 3.2 per g.