No abstract

Numerous strains of lactic acid bacteria associated with food systems are capable of producing bacteriocins, or antibacterial proteins with activity against foodborne pathogens such as Listeria monocytogenes, Staphylococcus aureus, and Clostridium botulinum. Recently, considerable emphasis has been placed on the identification of these proteins and their biochemical properties, including spectrum of activity, production conditions, purification procedures, amino acid composition, amino acid sequence, and modes of action. Advances in genetic engineering techniques have facilitated the characterization of these proteins at. the genetic level, providing information on hydropathic index, protein synthesis and structure, immunity determinants for resistance and/or tolerance, and cloning of bacteriocin genes into other organisms. Prior to the utilization of bacteriocins and/or the producer organism in food systems, a thorough understanding of the physical, biochemical, and genetic properties is required. Additional parameters for use of bacteriocins and bacteriocin-producing organisms in food systems also are discussed.

Well before the existence of starter bacteria was recognized, their activities were instrumental in preserving dairy foods. During growth in fermented products, dairy starters, including lactobacilli, lactococci, leuconostocs, streptococci, and propionibacteria, produce inhibitory metabolites. Inhibitors include broad-spectrum antagonists, organic acids, diacetyl, and hydrogen peroxide. Some starters also produce bacteriocins or bactericidal proteins active against species that usually are related closely to the producer culture. Several bacteriocins have been biochemically and genetically characterized. Evaluating properties of the Lactobacillus acidophilus bacteriocin, lactacin B, led to a new purification protocol. Purified lactacin B migrates in SDS-PAGE as a single 8100-Da band with inhibitory activity after Coomassie blue staining. Production of lactacin B is enhanced by cultivation of the producer with the sensitive indicator, Lactobacillus delbrueckii ssp. lactis 4797; understanding this interaction may increase knowledge of production of bacteriocins in heterogeneous cultures. Bacteriocins have been recently identified in dairy propionibacteria. Jenseniin G, a bacteriocin produced by Propionibacterium jensenii P126, has narrow activity; propionicin PLG-1 produced by Propionibacterium thoenii P127 inhibits propionibacteria, some fungi, Campylobacter jejuni, and additional pathogens. Better understanding of these antagonists may lead to targeted biocontrol of spoilage flora and foodborne pathogens.