Mechanism of action of antilisterial peptides produced by Lactobacillus sakei 2a, a bacteriocin strain isolated from brasilian meat product

LIMA, K. G. C.; KRUGER, M. F.; BARBOSA, M.S.; SALVUCCI, E.; SESMA, F.; FRANCO, B. D. G. M.

Florida

Congreso; IAFP 94th annual Meeting; 2007

IAFP

Bacteriocins produced by lactic acid bacteria (LAB) are gaining increased importance due to their activity against undesirable microorganisms, especially Listeria monocytogenes, an important psichrotrophic foodborne pathogen. In previous reports, we have shown that strain Lactobacillus sakei subsp. sakei 2a, isolated from a Brazilian pork meat product, presents antilisterial activity in vitro and in situ. Recently we demonstrated that L. sakei 2a produces sakacin 2a and at least other eight antilisterial peptides, all active against Enterococcus faecium, Enterococcus faecalis, Staphylococcus epidermidis, Lactococcus lactis, Enterococcus hirae, Enterococcus canis, Listeria monocytogenes and Listeria inoccua. It is known that Class II bacteriocins act by altering the permeability barrier of the cellular membrane of the target cells and one of the common mechanisms of inhibition is the dissipation of the membrane potencial. In this study we report results on the mechanism of action of the peptides produced by L. sakei 2a, by means of measuring the dissipation of membrane potencial (DY) and the depletion of intracellular pH (DpH) of L. monocytogenes using fluorescent probes, 3,3 dipropylthiocarbocyanine iodide [DiSC3(5)] and 2,7-bis-(2carboxyethyl)5(and 6)carboxyfluorescein (BCECF), respectively (Molecular Probes). The increase of flourescence of treated L. monocytogenes cells was measured. All peptides decreased the membrane potential and dissipated the DpH of L. monocytogenes in a concentration-dependent model: 10 nM of sakacin 2a caused the same effect as 100 nM of any of the other peptides  These results indicate that the antagonist activity of L. sakei subsp. sakei 2a can be attributed to different peptides presenting a similar mechanism of action, the same described for Class II bacteriocins. Acknowledgements: FAPESP and CNPq.