Enterocins Produced by Enterococci Isolated from Breast-Fed Infants: Antilisterial Potential

Enterocins are bacteriocins synthesized by Enterococcus strains that show an interesting antimi-crobial effectiveness against foodborne pathogens such as Listeria monocytogenes. The objectives of this study were identify and analyze the expression of enterocin genes of Enterococcus isolated from breast-fed infants and evaluate the ability to inhibit three human isolates of virulent Lis-teria monocytogenes, as well as some probiotic bacteria. The susceptibility of the strains of L. mon-ocytogenes to fifteen antibiotics was tested, detecting resistance to cefoxitin (constitutive-ly resistant), oxacillin and clindamycin. Production of enterocins A, B and P were observed in Enterococcus faecium isolates, and enterocin AS-48 in an Enterococcus faecalis isolate. AS-48 showed antilisterial activity by itself, while the joint action of enterocins A and B, or B and P was neces-sary for inhibiting L. monocytogenes, demonstrating a synergistic effect of those combinations. The presence of multiple enterocin genes does not assured the inhibition of L. monocytogenes strains. However, the expression of multiple enterocin genes showed a good correlation with the inhibition capacity of these strains. Furthermore the potential beneficial strains of lactobacil-li and bifidobacteria examined were not inhibited by any of the enterocins produced individu-ally or in combination, with the exception of Bifidobacterium longum BB536, which was inhibited by enterocin AS-48 and the joint production of enterocins A and B or B and P. The enterocins studied here could be candidates for developing alternative treatments against antibi-otic-resistant bacterial infections. Moreover, these selected enterocin-producing E. faecium strains isolated from breast-fed infants could be used as probiotic strains due to their antilisterial effect as well as the absence of virulence factors.