Characterization of Enterococcus faecium SP15, a novel isolate with probiotic and therapeutic potential

To characterise the genome and enterocin content of Enterococcus faecium SP15, a new isolate from natural spring water.

Enterococcus faecium strain SP15 was isolated from natural spring water and its identity confirmed using 16S rDNA sequence. The bacterial strain produced antimicrobial compounds (enterocins) against pathogenic bacteria including Listeria monocytogenesis as determined by the agar spot method. In addition, an anti-cancer activity was observed on human cancer cell line HT-29 by cytotoxicity assay (MTT) and apoptosis study. A draft genome sequence revealed the presence of several enterocin genes capable of activity against a panel of pathogenic bacteria including L. monocytogenesis. The active production of enterocins was also supported by the presence of peptides in part purified fermentates following trypsin digest and mass spectrometry. The genome showed no classical virulence factors or hemolysins and was free of antibiotic resistance genes. To confirm enterocin related killing, select enterocin genes were cloned and expressed as His-tagged proteins in E. coli. Purified enterocin retained activity in L. monocytogenes overlay assay.

E. faecium SP15 is a promising strain for probiotic use and/or food preservation. Purified enterocins retain their activity suggesting them a template for structure-function studies and future improvements as antimicrobial and cancer cell therapeutics. Significance and Impact of the Study: New antibacterial and anticancer agents are required to combat antibiotic resistance and a limited drug repertoire. Enterocins from Enterococcus faecium SP15 could fulfil these goals in addition to use of the strain as a whole organism probiotic.