The food-borne pathogenic bacterium Listeria is known for relatively low morbidity and high mortality rates, reaching up to 25 to 30%. Listeria is a hardy organism, and its control in foods represents a significant challenge. Many naturally occurring compounds, including the bacteriocin nisin and a number of plant essential oils, have been widely studied and are reported to be effective as antimicrobial agents against spoilage and pathogenic microorganisms. The aim of this study was to investigate the ability of semipurified preparations (SPP) containing either nisin A or an enhanced bioengineered derivative, nisin V, alone and in combination with low concentrations of the essential oils thymol, carvacrol, and trans-cinnamaldehyde, to control Listeria monocytogenes in both laboratory media and model food systems. Combinations of nisin V-containing SPP (25 g/ml) with thymol (0.02%), carvacrol (0.02%), or cinnamaldehyde (0.02%) produced a significantly longer lag phase than any of the essential oil-nisin A combinations. In addition, the log reduction in cell counts achieved by the nisin V-carvacrol or nisin V-cinnamaldehyde combinations was twice that of the equivalent nisin A-essential oil treatment. Significantly, this enhanced activity was validated in model food systems against L. monocytogenes strains of food origin. We conclude that the fermentate form of nisin V in combination with carvacrol and cinnamaldehyde offers significant advantages as a novel, natural, and effective means to enhance food safety by inhibiting food-borne pathogens such as L. monocytogenes.
The growing consumer demand for food products that are minimally processed and free of chemical preservatives presents a difficult challenge for food processors. Consequently, there has been a focus on the application of naturally produced antimicrobial compounds as a more acceptable means to control the growth of undesirable microorganisms in food (1, 2). Bacteriocins (ribosomally produced, small, heat-stable peptides that are active against other bacteria) derived from organisms generally regarded as safe provide one potential solution. However, only two bacteriocins have been made commercially available to any extent. These are nisin, produced by Lactococcus lactis, and pediocin PA-1, produced by Pediococcus acidilactici (3, 4). Of these, nisin is used in a wide variety of dairy and nondairy products, including cream and cheese products, soups, liquid egg, mayonnaises, salad dressings, tomato products, and beer (5). Nisin A exhibits antibacterial activity against a wide range of Gram-positive bacteria, including food-borne pathogens such as staphylococci, bacilli, clostridia, and Listeria (6, 7). Indeed, the success of nisin A from discovery (8) through to regulatory approval and finally to commercial application has spurred researchers to exploit its geneencoded nature and to attempt to "bioengineer" variants with altered biological, chemical, and physical properties. Over the last decade, several studies have described the discovery of new nisi...