Freezing effects on survival ofListeria monocytogenes in artificially contaminated cold fresh-salmon

摘要

The effects of freezing at ?20 °C were examined on surviving ofListeria monocytogenes contaminating food during freezing. Slices of fresh salmon were inoculated with three strains ofListeria monocytogenes (108 CFU/g). The inoculated pieces of fish were dried for 1 h at 24 °C and then stored in closed containers at ?20 °C for ten months. The identification of atypical cells found after freezing was achieved by PCR. This technique was based on the amplification of two specific genes ofL. monocytogenes hlyA andiap. The results showed that after ten months of frozen storage, the concentration ofL. monocytogenes determined on Trypticase Soya agar-Yeast Extract had declined by 2.39±0.01 log CFU/g and 2.22±0.01 log CFU/g for the strains isolated from meat, S1 and S2 respectively, and by 3.69±0.03 log CFU/g for the reference strain. The effect of frozen storage ofL. monocytogenes in salmon did not decrease the potential survival of food-borne pathogens’ over a period of ten months.