Contents 15.1 Introduction ................................................................................................................... 286 15.2 Low Molecular Weight Organic Compounds with Antimicrobial Activity .................... 286

15.2.1 Organic Acids ..................................................................................................... 286 15.2.2 Reuterin and Reutericyclin ................................................................................. 286 15.2.3 Antifungal Peptides from LAB ........................................................................... 287

15.3 Bacteriocins .................................................................................................................... 288 15.3.1 Lantibiotics ......................................................................................................... 288

15.3.1.1 Genes and eir Function .................................................................... 289 15.3.1.2 Modification ..........................................................................................291 15.3.1.3 Lantibiotic Immunity ........................................................................... 292 15.3.1.4 Diversity, Structure, and Mode of Action ............................................. 292

15.3.2 Nonlantibiotics (Class II) .....................................................................................293 15.3.2.1 IIa Bacteriocins ......................................................................................293 15.3.2.2 Two-Peptide Bacteriocins ...................................................................... 298 15.3.2.3 Diversity, Structure, and Mode of Action ............................................. 299 15.3.2.4 Bacteriocins without an N-Terminal Leader Sequence .......................... 300 15.3.2.5 Cyclic Bacteriocins................................................................................ 300 15.3.2.6 Truncated Antimicrobial Peptides ........................................................ 303

15.3.3 Targets and Mode of Action ............................................................................... 303 15.3.4 Regulation of Bacteriocin Biosynthesis ............................................................... 305 15.3.5 Bacteriocins Resistance and Adaptation .............................................................. 308 15.3.6 Application of Bacteriocins and Bacteriocin-Producing LAB ...............................310 15.3.7 Additional Aspects Concerning Bacteriocins .......................................................310

15.4 Concluding Remarks ......................................................................................................311 References ................................................................................................................................311

15.1 Introduction Lactic acid bacteria (LAB) have been used in the household since ancient times owing to their ability to produce and preserve foods. LAB have been shown to be superior to other microorganisms in fulfilling the role of food and feed preservatives, although other organisms have also found a place in more defined products. LAB constitute a diverse group of bacteria that are widely distributed throughout nature, including being an important constituent of the healthy indigenous microflora in humans and animals. Within the LAB group, the genus Lactobacillus is the most widely encountered among probiotics because members of this genus display antimicrobial activities. ey produce a number of antimicrobial metabolites, including organic acids, other organic compounds, hydrogen peroxide, and bacteriocins. Food-grade LAB meet the requirements of being ideal microbial food biopreservatives because they have been proven to be nontoxic to humans, they do not alter nutritional properties of the food, they are effective at low concentrations, they are active under refrigerated storage, and they are even considered to possess healthpromoting effects. is review will first provide a short description of the low molecular weight, organic antimicrobial metabolite components that are produced by LAB, followed by a more detailed overview of the more complex bacteriocins produced by LAB. Bacteriocins have received considerable interest because of their potent antibacterial activities that apply to the areas of food and health, and also because they are a means of fighting antibiotic-resistant bacteria.