Behaviour of Listeria monocytogenes in raw sausages (merguez) in presence of a bacteriocin-producing lactococcal strain as a protective culture.

The effectiveness of a bacteriocin produced by Lactococcus lactis subsp. lactis M in reducing population level and growth of Listeria monocytogenes ATCC 7644 in fermented merguez sausage was examined. Two different formulas (with or without added nitrites) were assayed and predetermined numbers of Listeria (ca 10(6) cfu g(-1)) were added to sausage mixture. The effect of in situ production of the bacteriocin by Lactococcus lactis M on Listeria monocytogenes ATCC 7644 during fermentation and storage of merguez sausages at room (ca 22 °C) or at refrigeration (ca 7 °C) temperature was tested. Results indicated that counts of Listeria monocytogenes were decreased during fermentation of merguez samples fermented with either the bacteriocin-producing Lactococcus lactis M (Bac(+)) or a nonbacteriocin-producing Lactococcus lactis J (Bac(-)). However, reduction in Listeria cfu's was greater in samples fermented with the Bac(+) than in those fermented with the Bac(-) starter. In merguez sausage made without nitrites addition, the Bac(+) starter induced further decrease in Listeria counts by 1.5 log cycles compared with that induced by the Bac(-) starter. While in merguez samples with added nitrites (0.4%), the effect of the bacteriocin produced in situ was less important than in those made without nitrites addition.