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.

Aims:  To investigate the in vivo gene transfer of high‐level gentamicin resistance (HLRG) from Enterococcus faecalis isolated from the food of animal origin to a human isolate, using a mouse model of intestinally colonized human microbiota. Methods and Results:  In vitro study: The presence of plasmids involved in HLRG coding was investigated. After the conjugation experiment, the recipient strain, Ent. faecalis JH2‐SS, acquired a plasmid responsible for HLRG [minimal inhibitory concentration (MIC) >800 μg ml−1], in a similar position to the donor cells. In vivo study: Seven BALB/c mice were dosed with ceftriaxone (400 mg kg−1) and then inoculated with a dilution of 1/100 of human faeces (HFc). After 72 h, Ent. faecalis JH2‐SS (recipient) was inoculated and then, after a further 72 h, the animals were given Ent. faecalis CS19, isolated from the food of animal origin, involved in HLRG (donor). The presence of transconjugant strains in HFc was subsequently recorded on a daily basis until the end of the experiment. The clonal relationship between Ent. faecalis and Escherichia coli in faeces was assessed by RAPD‐PCR. Both the in vitro and in vivo studies showed that the receptor strain acquired a plasmid responsible for HLRG (MICs >800 μg ml−1), which migrated with a similar relative mobility value. Transconjugant strains were detected from 24 h after the donor strain inoculation and persisted until the end of the experiment. Conclusions:  The in vivo gene transfer of HLRG from Ent. faecalis strains, isolated from the food of animal origin, to human microbiota has been demonstrated in a mouse model. Significance and Impact of the Study:  The complexity found on the therapeutic responses of invasive infectious diseases caused by Ent. faecalis facilitates the assessment of food of animal origin as a resistant pathogen reservoir. In addition, this study may contribute to the understanding of antimicrobials’ resistance gene transfer between Ent. faecalis strains from food and human GI tract.

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