Bacteriocins of lactic acid bacteria: Recent data on their structure, their mode of action and their genetic determinants.

Bacteriocins of lactic acid bacteria (LAB) have been subjected to numerous studies starting 10 years ago because they are of major interest at both basic and applied levels. Bacteriocins are produced by numerous species of LAB and directed towards homologous or eventually heterologous (Listeria monocytogenes) strains. A classification has been proposed in accordance to their primary structures. Three classes have been defined, namely lantibiotics, small non lantibiotics and large size bacteriocins. Their mode of action has been analyzed. The current models are based on pore formation in the membranes of the target cells either by a direct insertion in the phospholipid bilayer (lantibiotics) or after an interaction with a putative protein receptor. in both cases, several bacteriocin molecules acting concomitantly are thought to be involved in pore formation. Genetic determinants for bacteriocin synthesis, production and immunity are present in more or less complex gene clusters. The simplest system leads to the synthesis of divergicin A (sec-dependent export) whereas other systems require dedicated export machineries (sec-independent export via ABC transporters). A better knowledge at the molecular level of the basic mechanisms for bacteriocin immunity, production and its regulation, and of the mode of action as well as emerging resistance is still necessary before envisaging extensive technological applications in milk or meat products.