PhD thesis of Yanath Belguesmia (2007-2010)

Food safety and hygiene is a major concern of modern societies. The development of pathogenic bacteria in foods such as Camplyobacter jejuni and Listeria monocytogenes requires research into new methods of controlling these microorganisms. Bacteriocins produced by lactic acid bacteria are an interesting alternative that should be further explored and promoted. In this thesis, we focused on the chicken digestive ecosystem in order to isolate new bacteriocinogenic lactic acid bacteria. Our study shows a predominance of the genus Lactobacillus. Among the bacteriocinogenic lactic acid bacteria identified, there is Enterococcus faecalis S37 which exhibits strong anti-Listeria and anti-Campylobacter activity. This activity is attributed to the production of a bacteriocin called enterocin S37. We purified enterocin S37 by chromatographic methods and characterized its mode of action. Enterocin S37 has a molecular weight of between 4 and 6 kDa, it is resistant to heat treatment and extreme pH. It is mainly active against strains of Listeria monocytogenes and Enterococcus faecalis. The mode of action of enterocin S37, studied through the use of potassium channel modulators, has shown an interaction with ATP dependent potassium channels causing the leakage of K + ions and intracellular ATP molecules. Furthermore, the safety of enterocin S37 has been demonstrated in a differentiated Caco-2 / TC7 enterocytic cell model, making this bacteriocin a potential candidate for use in the prevention of these microorganisms. We have also shown that the combination of nisin A and / or pediocin PA-1 with polymyxin E allows an additive and / or synergistic effect on resistant strains of Listeria monocytogenes.