Suitability of Lactococcus lactis subsp lactis ATCC 11454 as a protective culture for lightly preserved fish products

This study is part of strategy to control the human pathogen Listeria monocytogenes in lightly preserved fish products by using food-grade lactic acid bacteria. When the nisin-producing Lactococcus lactis subsp lactis ATCC 11454 was cultured in the same vessel as L-monocytogenes Scott A in brain-heart infusion broth (BHI) at 30-degrees C, the pathogen declined from 5x10(5) to fewer than 5 cfu ml(-1) within 31 h. The effect was not due to lactic acid inhibition. Growth and nisin production by L-lactis ATCC 11454 were investigated under the conditions of temperature and salt used for light preservation. At 5-degrees C in M17 broth, the organism grew well ans produced nisin. In an infusion of cold-smoked salmon the organism did not grow at 5-degrees C, althoigh it did at 10-degrees C. NACl up to 4% allowed for efficient growth and nisin production, while 5% NaCl resultes in very slow growth and no detectable nisin. On slices of commercial cold-smoked salmon at 10-degrees C, no net propagation pf L-lactis ATCC 11454 could be detected within 21 days. However, when salmon slices were inoculated with L-mycocytogenes at 10(4) cfu g(-1) and a 300-fold excess of washed lactococcus cells, the pathogen's population declined a half log the first 1-5 days, then increased at a rate slightly lower than that of the control not inoculated with the lactococcus.