Inhibition of Listeria monocytogenes by a formulation of selected dairy starter cultures and probiotics in an in vitro model

Abstract

Three strains of lactic acid bacteria (LAB) and a commercial probiotic were selected to evaluate their in vitro activity towards Listeria monocytogenes. The strains Lactococcus lactis ssp. lactis, strain 340, L. lactis ssp. lactis, strain 16; Lactobacillus casei ssp. casei, strain 208 and Enterococcus faecium UBEF-41 were inoculated into skim milk and brain heart infusion broth (BHI) to get an initial Lactococcus: Lactobacillus: E. faecium UBEF-41 ratio of 2:1:1 and a concentration of approximately 7 log cfu mL−1 until challenge vs. pathogen. L. monocytogenes ATCC 7644 was also inoculated in same media to get approximately 4 log cfu mL−1. Growth curves in skim milk and BHI at 4, 10 and 30 °C, respectively were studied for: (i) LAB formulation; (ii) L. monocytogenes and (iii) LAB vs. L. monocytogenes. When challenged with LAB, at 30 °C in milk, L. monocytogenes was not detectable after day-3 and in BHI it decreased below log cfu mL−1 after day-5. At 10 and 4 °C, in both media, L. monocytogenes counts were always significantly lower (p