The potential influence of two Enterococcus faecium on the growth of Listeria monocytogenes

Two strains of Enterococcus faecium isolated from meat products were analyzed for the antimicrobial activity, safety and inhibition of Listeria monocytogenes in co-culture experiments. The production of bacteriocin-like substances and the presence of enterocin A, B, P genes (entA, entB, entP) were confirmed in E. faecium B1 whilst E. faecium B2 harbored neither of these characteristics. None of E. faecium strains harbored the virulent determinants studied (esp, hylEfm, IS 16, VanA and VanB) and were sensitive to most common antibiotics. In the co-culture experiment, both E. faecium B1 and E. faecium B2 had an inhibition effect towards L. monocytogenes. However, E. faecium B1 inhibited the growth of L. monocytogenes in the early stages of co-culture, and then probably reduced the cell counts of L. monocytogenes until an undetectable level after four days. Thus the cell counts of L. monocytogenes stayed at the initial inoculum level during the co-culture with E. faecium B2, suggesting that the bacteriocin-like substance played an important role in the inhibition effect. Meanwhile, the pH in co-culture declined lower than that in mono-culture in the early days, indicating the production of acid might participate in the inhibition process. Also, E. faecium B1 could be considered to be used as an effective potential bio-protective culture, so as to improve the safety of meat products.