Aims:  To assess the inhibitory activity on Gram‐positive and Gram‐negative bacteria of several species of enterococci recovered from a natural corn silage. Methods and Results:  The inhibitory activity of strains of Enterococcus faecalis (58), Enterococcus faecium (35), Enterococcus gallinarum (3) and Enterococcus casseliflavus (4) were studied employing indicator strains from various sources (clinical, food and ATCC). Enterococcus faecalis MR99, the only strain with inhibitory activity, inhibited other enterococci, Listeria spp., Staphylococcus aureus, Clostridium spp., Bacillus spp., Escherichia coli, Shigella sonnei and Shigella flexneri. The bacterium contained only one conjugative pheromone‐responsive plasmid. The partially chromatography‐purified MR99 enterocin (PPE) had a molecular weight of approx. 5000 Da and a pI of 6·2, was sensitive to proteolytic enzymes and could be extracted in benzene and butanol. It appeared stable to adjustment of pH 4·0, 5·0, 6·0, 7·0 and 8·0 and was resistant to heat. Inactivation was at 15 min at 121°C. Enterocin MR99 was bactericidal on strains of Listeria monocytogenes, Staph. aureus, and bovine mastitis agents, it was bacteriostatic on E. coli. Although enterocins MR99 and AS48 have inhibitory activity on Gram‐negative bacilli, PCR studies demonstrated a lack of relationship between them. Conclusions:  The active component had a protein nature, was resistant to heat and presented a wide inhibitory spectrum. Significance and Impact of the Study:  The biological properties of Ent. faecalis MR99 suggest that this strain merits further investigations so it can be applied in human and veterinary health programmes.

Probiotics can modulate the immune system, conferring beneficial effects on the host. Understanding how these microorganisms contribute to improve the health status is still a challenge. Previously, we have demonstrated that Enterococcus faecalis CECT7121 implants itself and persists in the murine gastrointestinal tract, and enhances and skews the profile of cytokines towards the Th1 phenotype in several biological models. Given the importance of dendritic cells (DCs) in the orchestration of immunity, the aim of this work was to elucidate the influence of E. faecalis CECT7121 on DCs and the outcome of the immune responses. In this work we show that E. faecalis CECT7121 induces a strong dose-dependent activation of DCs and secretion of high levels of IL-12, IL-6, TNFα, and IL-10. This stimulation is dependent on TLR signaling, and skews the activation of T cells towards the production of IFNγ. The influence of this activation in the establishment of Th responses in vivo shows the accumulation of specific IFNγ-producing cells. Our findings indicate that the activation exerted by E. faecalis CECT7121 on DCs and its consequence on the cellular adaptive immune response may have broad therapeutic implications in immunomodulation.

No abstract