Bacteriocins

It has long been known that lactic acid bacteria are antagonistic to other microorganisms through production of antimicrobial compounds such as hydrogen peroxide, acetic acid, lactic acid, and diacetyl. However, these and other food fermentation microorganisms also produce peptide antimicrobial compounds known as bacteriocins. Bacteriocins are bactericidal to susceptible genera or species and are often produced under plasmid control. These compounds are not considered to be antibiotics as they are not used for human disease control, are larger than medical antibiotics, and usually have a narrow spectrum. Potentially useful bacteriocins have been demonstrated from Lactococcus, Lactobacillus, Pediococcus, Leuconostoc, Propionibacterium, Bifidobacterium, and Carnobacterium. Although none of the compounds are approved for use in foods, there is great potential for their use in the future. Most of the bacteria that produce bacteriocins being considered as food antimicrobials are used or associated with fermented dairy, meat, and vegetables products. For that reason, the antimicrobials they produce would be assumed to be safe from a toxicological standpoint. Many bacteriocins have been isolated and their effectiveness characterized in microbiological media, but much work remains to be done on determining their effectiveness in foods.

Excluding nisin, the most well characterized bacteriocins are those produced by Pediococcus species. Pediococcus acidilactici produces pediocin AcH and PA-1, and P. pentosaceus produces pediocin A. Pediocin AcH and PA-1 inhibit Bacillus, Brochothrix, Clostridium, Enterococcus, Lactobacillus, Leuconostoc, Listeria monocytogenes, other Pediococcus, Propionibacterium, and Staphylococcus aureus. Pediocin A is inhibitory to other lactic acid bacteria and the pathogens Bacillus cereus, Clostridium botulinum, C. perfringens, L. monocytogenes, and S. aureus. Gramnegative bacteria can be made to be susceptible to pedi-ocins following exposure to sublethal stress treatments such as freezing or heat (61). In foods, pediocin AcH inhibits spoilage bacteria in meats, dairy products, salads, and salad dressings, and it has a variable effect on growth of pathogens inoculated into foods (61). Limitations on the use of pediocins in foods include: (1) it may cause resistance development in some microorganisms; (2) it may select for resistant strains in foods; and (3) food components, especially lipids, could interfere with antimicrobial activity (61).

Several species of Lactobacillus have been shown to elucidate bacteriocins. These include L. acidophilus, L. brevis, L. casei, L. delbrueckii ssp. bulgaricus, L. fermentum, L. helveticus, L. plantarum, andL. sake (18,61). Bacteriocins produced by Leuconostoc include those produced by L. car-nosum, L. dextranicum, L. gelidum, L. mesenteroides, and L. paramesenteroides. Various of these bacteriocins have shown activity against C. botulinum, L. monocytogenes, S. aureus, and Yersinia enterocolitica (61). Carnobacterium piscicola and Bifidobacterium have shown to produce bacteriocins with activity primarily against gram positive bacteria including L. monocytogenes. Milk fermented by Propionibacterium freudenreichii ssp. shermanii is effective against Gram-negative psychrotrophic bacteria in cottage cheese and spoilage microorganisms in a variety of other foods. Among the inhibitors in this product are propionic acid, lactic acid, and a low-molecular-weight proteinaceous compound (74).

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