Enterococcus mundtii ST4SA and Lactobacillus plantarum 423 excludes Listeria monocytogenes from the GIT, as shown by bioluminescent studies in mice.

Listeria monocytogenes is an opportunistic food-borne pathogen and is life-threatening to individuals with a weakened immune system. The aim of this study was to determine if Lactobacillus plantarum 423 and Enterococcus mundtii ST4SA could prevent colonisation of L. monocytogenes in the gastro-intestinal tract (GIT). Mice were gavaged with L. plantarum 423, E. mundtii ST4SA, and a combination of the two strains, for 6 consecutive days and orally infected with a bioluminescent strain of L. monocytogenes (strain EGDe) on the last day of treatment. 30 min after infection, high cell numbers of L. plantarum 423, E. mundtii ST4SA and L. monocytogenes EGDe were isolated from faeces. L. monocytogenes EGDe cells were absent from the small intestine of L. plantarum 423-treated mice 4 h after infection and from the large intestine 2 h later. No bioluminescent, and thus metabolically active, cells of L. monocytogenes EGDe were recorded in the GIT of mice treated with E. mundtii ST4SA, suggesting that their growth was repressed. L. plantarum 423 and E. mundtii ST4SA colonised the colon the strongest. These strains may be considered for the competitive exclusion of L. monocytogenes from the GIT.