Abstract
Mesophilic strains of lactic acid bacteria belonging to the genus Lactococcus were isolated from traditional dairy products and selected for their ability to produce antimicrobial substances such as bacteriocins. Six strains: Lactococcus lactis ssp. lactis (strains Lc l1, Lc l3, Lc l5), Lactococcus lactis ssp. cremoris (strains Lc c4, Lc c6) and Lactococcus lactis ssp. lactis biovar diacetylactis (strain Lc d2) were selected for their antagonistic activities against different groups of microorganisms. The most active strain, Lactococcus lactis ssp. lactis (Lc l5), produced its inhibitory substance (Bac5) in M17 broth presenting an important inhibition mainly against Listeria monocytogenes. It had no effect on its producer strain. These properties suggested that the inhibitory substance could be considered as a bacteriocin-like substance. SDS-PAGE analyses indicated that it was a homogeneous protein of higher molecular weight of 67 kDa. The bacteriocin was stable over a wide range of pH and temperature; it was active after autoclaving and was not affected by storage at −20°C for 6 months. Moreover, it was sensitive to proteolytic enzymes confirming the proteinaceous nature of the inhibitory substance.
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