Common mechanism of action of bacteriocins from lactic acid bacteria

Bacteriocins from Generally Recognized as Safe (GRAS) lactic acid bacteria (LAB) may provide a novel approach to control Listeria monocytogenes in minimally processed refrigerated foods. Although a great deal of research is centered on the characterization and putative food applications of LAB bacteriocins, little is known about the fundamental mode of action of these antimicrobial proteins. The objective of this research was to elucidate the mechanisms by which LAB bacteriocins inhibit sensitive organisms, with particular interest in L. monocytogenes.; The bacteriocin literature led us to the hypothesis that LAB bacteriocins share a common and powerful mechanism of action which is the dissipation of the proton motive force (PMF) of sensitive organisms. To test the PMF depletion hypothesis, the influence of nisin, pediocin PA-1 and leuconocin S on the PMF of L. monocytogenes Scott A cells was investigated. In contrast to a previous report, lactacin F was not effective against L. monocytogenes FRI-LM 103M. Thus, the effect of this bacteriocin on PMF was determined on its most sensitive indicator strain, Lactobacillus delbrueckii ATCC 4797. Nisin (2.5 {dollar}mu{dollar}g/ml), pediocin PA-1 (20 {dollar}mu{dollar}g/ml) and leuconocin S (48.5 {dollar}mu{dollar}g/ml) mediated total or major PMF dissipation of energized L. monocytogenes Scott A cells in a concentration-dependent manner. Lactacin F (13.5 {dollar}mu{dollar}g/ml) caused 87% PMF depletion of energized L. delbrueckii ATCC 4797 cells, also in a concentration-dependent fashion.; The energy requirements for the activity of these four bacteriocins were determined using the ionophores nigericin and valinomycin which produce partial and specific deenergization of the target organisms. Pediocin PA-1, leuconocin S and lactacin F acted in an energy-independent manner, whereas the activity of nisin was confirmed to be energy-dependent. This is important when potential applications of bacteriocins as antimicrobial agents are taken into account. As food preservatives, energy-dependent or energy-independent bacteriocins may be equally effective. This is because in a rich and complex food system the target cells for bacteriocin action are expected to be active metabolizing cells which maintain fully energized cytoplasmic membranes. On the other hand, energy-independent bacteriocins would be more effective as sanitizers for use in plant facilities. Under these circumstances target cells are most likely non-growing resting cells that maintain lower levels of metabolic activity and consequently partially energized membranes.; LAB bacteriocins act by the common mechanism of PMF depletion and can be divided into energy-dependent or energy-independent. These results establish the similarity of LAB bacteriocins to other PMF-depleting antimicrobial proteins such as colicins and defensins.