ANTIBIOSIS REVISITED - BACTERIOCINS PRODUCED BY DAIRY STARTER CULTURES

Well before the existence of starter bacteria was recognized, their ac tivities were instrumental in preserving dairy foods. During growth in fermented products, dairy starters, including lactobacilli, lactococc i, leuconostocs, streptococci, and propionibacteria, produce inhibitor y metabolites. Inhibitors include broad-spectrum antagonists, organic acids, diacetyl, and hydrogen peroxide. Some starters also produce bac teriocins or bactericidal proteins active against species that usually are related closely to the producer culture. Several bacteriocins hav e been biochemically and genetically characterized. Evaluating propert ies of the Lactobacillus acidophilus bacteriocin, lactacin B, led to a new purification protocol. Purified lactacin B migrates in SDS-PAGE a s a single 8100-Da band with inhibitory activity after Coomassie blue staining. Production of lactacin B is enhanced by cultivation of the p roducer with the sensitive indicator, Lactobacillus delbrueckii ssp. l actis 4797; understanding this interaction may increase knowledge of p roduction of bacteriocins in heterogeneous cultures. Bacteriocins have been recently identified in dairy propionibacteria. Jenseniin G, a ba cteriocin produced by Propionibacterium jensenii P126, has narrow acti vity; propionicin PLG-1 produced by Propionibacterium thoenii P127 inh ibits propionibacteria, some fungi, Campylobacter jejuni, and addition al pathogens. Better understanding of these antagonists may lead to ta rgeted biocontrol of spoilage flora and foodborne pathogens.