Interaction between Lactococcus lactis strains and Listeria monocytogenes in mixed cultures

Szigeti, E. (2001) Interaction between Lactococcus lactis strains and Listeria monocytogenes in mixed cultures. Acta Alimentaria, 30 (3). pp. 247-265. ISSN 0139-3006

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Abstract

Competition between a bacteriocinogenic and a non-bacteriocinogenic Lactococcus lactis strain, respectively, and a Listeria monocytogenes strain was studied in two semi-synthetic liquid media at various temperatures. The media used for the study were ST I and modified ST I broth (ST I broth + 1 g l-1 Tween 80). In both media, at 30 °C, a significant cell count reduction (5 log) of L. monocytogenes occurred only when the cell concentration of the bacteriocinogenic competitor reached the level of at least 107 CFU ml-1 required for the production of sufficient concentration of nisin-like bacteriocin. The same phenomenon was also observed when the initial level of the lactic acid bacteria (LAB) was one log higher or lower than that of the Listeria, however, the reduction of Listeria cell count occurred earlier with the higher initial concentration of the LAB. Incubation of the mixed cultures at 20 °C gave similar results but the bacteriocinogenic activity resulted in only a three log decline of the cell count of L. monocytogenes. At 10 °C Lactococcus lactis produced much less bacteriocin than at 30 °C, therefore, a drastic decrease of the Listeria cell count was not observed. Suppression of the Listeria growth was expressed in its decreased maximum population level (i.e. in an earlier appearance of the stationary phase). When the non-bacteriocinogenic Lac. lactis and Listeria were present at the same initial level (approx. 105 CFU ml-1), the Lactococcus did not affect the growth of L. monocytogenes at 30 °C in modified ST I broth.

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