This study investigated the antimicrobial activity of Enterococcus faecium FAIR-E 198 against Bacillus cereus, Listeria monocytogenes and Staphylococcus aureus. Using the critical-dilution method, the bacteriocin produced by E. faecium FAIR-E 198 inhibited all L. monocytogenes strains evaluated (1,600 to 19,200 AU mL(-1)). However, none of the B. cereus and S. aureus strains investigated were inhibited. The maximum activity of this bacteriocin (800 AU mL(-1)) was observed in MRS broth, while the activity in milk was 100 AU mL(-1). In the co-cultivation test in milk, B. cereus K1-B041 was reduced to below the detection limit (1.00 log CFU mL(-1)) after 48 h. E. faecium reduced the initial L. monocytogenes Scott A population by 1 log CFU mL(-1) after 3 h at 35°C, However, the pathogen regained growth, reaching 3.68 log CFU mL(-1) after 48 h. E. faecium did not influence the growth of S. aureus ATCC 27154 during the 48 h of co-cultivation, Therefore, it can be concluded that the effectiveness of the antimicrobial activity of E. faecium FAIR-E 198 is strictly related to the species and strain of the target microorganism and to the culture medium.