Enterococci from breast-fed infants exert higher antibacterial effects than those from adults: A comparative study

Enterococci are members of human gut microbiota which their colonization has been demonstrated even before birth. This indicates their importance in infant health. As this population is dynamic and varies with age, this study was designed to assess and compare the antibacterial effects of enterococci from breast-fed infants and those from adults. Fecal isolates of enterococci were isolated from infants and healthy adults and were identified to the species level by phenotypic and genotypic methods. Further, they were evaluated for their potential to exert antibacterial effect against ten standard bacterial strains using bilayer spot test. Of a total of eighty-nine recovered enterococcal isolates, Enterococcus faecium and E. faecalis were the most common species (98%) and showed inhibitory effects at least against one indicator strain. Comparison between isolates from two studied groups showed that isolates from neonates introduced significantly higher growth inhibitory effects against six indicator strains (P < 0.05) and these effects were frequently attributable to E. faecium isolates. In addition, the highest growth inhibitory effect was observed against Listeria monocytogenes. Antimicrobial effects of enterococci in human microbiota change during time. The beneficial role of these organisms within the neonatal period suggests the potential of enterococci from breast-fed infants for probiotic application.