Enterococci comprise a major part of the natural microbiota of traditional cheeses. Enterocins may contribute to minimize survival or growth of Listeria monocytogenes in milk and cheese.
Purpose:
Enterococcus faeciumKE82, a multiple enterocin-producing strain isolated from traditional Greek Graviera cheese was assessed for antilisterial activity in milk, and possession of other desirable technological and probiotic properties.
Methods:
Sterile milk (SM)-used as a model system, or thermized (63oC, 15 sec) milk (TM) were inoculated with 3 to 4 log CFU/ml of L. monocytogenes.Contaminated milk portions (50 ml) were further inoculated with ca. 6 log CFU/ml of a commercial starter culture (CSC) and/or strain KE82. All milks were incubated at 37°C for 6 h and then at 18°C for an additional 42 h.
Results:
Listeria monocytogenes increased by 5 log units in SM, whereas in SM+CSC it increased by 2 log units within the first 12 h, but its further growth was minimized. In SM+CSC+KE82, a complete growth inhibition followed by progressive inactivation of L. monocytogenes (0.6 log CFU/ml at 48 h) populations was noted. L. monocytogenesincreased by 2 log units in TM, whereas in TM+CSC and TM+KE82 its growth was retarded within 6 to 12 h, and then ceased. In TM+CSC+KE82 the pathogen could not grow. When detected by PCR the enterocin genes A, B, and P gave a stronger signal in TM+KE82 than in TM samples, but weaker in TM+CSC+KE82 samples. Strain KE82 showed high survival under various challenging conditions simulating those of the gastrointestinal tract.
Significance:
Thus, E. faecium KE82 constitutes a promising adjunct culture in traditional cheese making since it concomitantly produces enterocins A, B and P in situin milk, and exhibits a high probiotic potential.
Acknowledgement: Part of this research was funded by ‘Research & Technology Development Innovation Projects’-AgroETAK.