Search

Lactobacillus casei CRL705 produces a class IIb bacteriocin, lactocin 705, which relies on the complementary action of two components, Lac705alpha and Lac705beta. These peptides exert a bactericidal effect on the indicator strain Lactobacillus plantarum CRL691, with an optimal Lac705alpha/Lac705beta peptide ratio of 1 to 4. Electron microscopy studies showed that treated CRL691 cells have their cell wall severely damaged, with mesosome-like membranous formations protruding into their cytoplasm. Although less pronounced, a similar effect was also observed with the Lac705beta peptide alone. Furthermore, Lac705beta increased the inhibitory action of a diluted supernatant of L. casei CRL705, while Lac705alpha protected CRL691 cells from inhibition. Both peptides were required to dissipate the proton motive force (Deltapsi and DeltapH) of CRL691 cells. These data suggested that of the two components of lactocin 705, the Lac705alpha peptide is responsible for receptor recognition, and the Lac705beta peptide is the active component on the cell membrane of CRL691 cells.

The antilisterial efficiency of three bacteriocins from lactic acid bacteria, lactocin 705 (produced by L. casei CRL705, 17000 AU/ml), enterocin CRL35 (produced by E. faecium CRL35, 17000 AU/ml), and nisin (2000 IU/ml), was tested in broth, individually and in combination against Listeria monocytogenes and Listeria innocua. Both Listeria species showed an initial decrease in viable counts followed by the regrowth of the survivors after 1 h in the presence of each bacteriocin. A greater antilisterial effect was observed when the bacteriocins were combined in pairs, maximal inhibition being reached when nisin was involved. When a mix of the three bacteriocins was used, no survivors were observed after 24 h of incubation. Similar results were obtained when the bacteriocin combinations were tested in a meat system, indicating that the use of more than one LAB bacteriocin in combination may be effective in preventing the spontaneous emergence of a bacteriocin-resistant Listeria population.