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 displayed interference in both compartments. Maximum bacteriocin production was observed at the end-logarithmic phase, with the exception of 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 strains were active only on List. monocytogenes, and the enterocin A amount was enhanced under oxygen stress. All L. lactis strains (including L. lactis subsp. cremoris EL3 generally producing nisin Z) biosynthesised 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: these strains can be employed in toto directly in the food matrix or the purified bacteriocins can be incorporated into food packaging.