Anti-S.aureus and anti-L.monocytogenes molecules produced by cheese-isolated lactic acid bacteria

Nine lactic acid bacteria from artisanal-made cheeses, were investigated for their ability to inhibit Listeria monocytogenes and Staphylococcus aureus. Both extracellular and surface-bound bacteriocins were recovered. While Lb. plantarum molecule was present only extracellularly, all the other strains display interference in both compartments. Maximum bacteriocin production was observed at the end-logarithmic/beginning stationary phase, exception made for Lb. plantarum (late stationary) and L. lactis subsp. cremoris (very early exponential). Lactobacillus and Lactococcus strains inhibited both List. monocytogenes and S. aureus. On the contrary, both E. faecium were active only on List. monocytogenes, and the bacteriocin (Enterocin A) amount was enhanced under oxygen stress. All L. lactis strains (including L. lactis subsp. cremoris EL3 generally producing Nisin Z) biosynthesized Nisin A, while Lb. plantarum caused interference because of its very high lactic acid production. All these results suggest that artisanal-made cheeses can contain promising strains for food biosafety: from one side these strains can be employed in toto directly in the food matrix, from the other side the purified bacteriocins can be incorporated into food packaging. This is of particular relevance when enterococci are concerned since their employment in food is questionable due to their possible virulence and antibiotic resistence.