An update on the taxonomy and functional properties of the probiotic Enterococcus faecium SF68

Abstract

Enterococcus faecium SF68 (SF68) is a well-known probiotic with a long history of safe use. Recent changesin the taxonomy of enterococci have shown that a novel species, Enterococcus lactis, is closely related with E.faecium and occurs together with other enterococci in a phylogenetically well-defined E. faecium species group.The close phylogenetic relationship between the species E. faecium and E. lactis prompted a closer investigationinto the taxonomic status of E. faecium SF68. Using phylogenomics and ANI, the taxonomic analysis in this studyshowed that probiotic E. faecium SF68, when compared to other E. faecium and E. lactis type and reference strains,could be re-classified as belonging to the species E. lactis. Further investigations into the functional properties ofSF68 showed that it is potentially capable of bacteriocin production, as a bacteriocin gene cluster encoding theleaderless bacteriocin EntK1 together with putative Lactococcus lactis bacteriocins LsbA, and LsbB-like putativeimmunity peptide (LmrB) were found located in an operon on plasmid pF9. However, bacteriocin expressionwas not studied. Competitive exclusion experiments in co-culture over 7 days at 37 °C showed that the probioticSF68 could inhibit the growth of specific E. faecium and Listeria monocytogenes strains, while showing little or noinhibitory activity towards an entero-invasive Escherichia coli and a Salmonella Typhimurium strain, respectively.In cell culture experiments with colon carcinoma HT29 cells, the probiotic SF68 was also able to strain-specificallyinhibit adhesion and/or invasion of enterococcal and L. monocytogenes strains, while such adhesion and invasioninhibition effects were less pronounced for E. coli and Salmonella strains. This study therefore provides novel dataon the taxonomy and functional properties of SF68, which can be reclassified as Enterococcus lactis SF68, therebyenhancing the understanding of its probiotic nature.