EFFECT OF THE TEMPERATURE ON THE ANTAGONISTIC ACTIVITY OF LACTIC ACID BACTERIA AGAINST ESCHERICHIA COLI AND LISTERIA MONOCYTOGENES

In this study the effect of refrigeration, abusive and optimum growth temperatures (5, 20, and 37C) on the dynamic of bacterial populations in pure and co-cultures was investigated. The antagonistic activity of two lactic acid bacteria (LAB) strains, with auto- and co-inducible bacteriocin-like inhibitory substance production, against Escherichia coli and Listeria monocytogenes was described and quantified through the comparison of the growth curves and the estimated kinetic parameters of pure and mixed cultures. The growth pattern of the bacterial binary systems studied showed that the mechanism of inhibition was complex and not attributable to one antagonist factor. Temperature had an effect on the spectrum of action and the level of inhibition of the growth of the pathogens by LAB. Low and suboptimal temperatures significantly reduced the antagonistic activity of the two LAB strains against the pathogenic bacteria. At refrigeration temperature only the growth of L. monocytogenes was inhibited by Lactobacillus plantarum WS4174. The results obtained show the importance of validating functionality of biological antimicrobial systems when used for biopreservation purposes under different application conditions. PRACTICAL APPLICATIONS Consumers demand the use of natural systems to provide safety foods with extended shelf life. Lactic acid bacteria (LAB) have demonstrated through thousands years their potential to control spoilage and pathogenic microorganisms and therefore suitable for biopreservation purposes. The antagonistic properties of LAB rely on the production of organic acids and antimicrobial peptides (bacteriocins) among other bioactive metabolites. However, there is need for more research in order to understand the mechanism of inhibition and to assess the effectiveness of LAB and/or of their growth-limiting metabolites under different conditions. LAB and their antimicrobial compounds, such as bacteriocins, are not necessarily functional in all food systems and environmental conditions. The present study shows how the fluctuation in bacteriocin-like inhibitory substances production and/or activity caused by temperature changes is reflected on the inhibition potential against Listeria monocytogenes and Escherichia coli. Effectiveness of biological control is essential for its safe and successful application on foods.