Purification and some characteristics of enterocin ON-157, a bacteriocin produced by Enterococcus faecium NIAI 157

Bacteriocin-like activity (BLA) was screened in 690 strains of lactic acid bacteria isolated from plant materials such as silages and fermented vegeta bles. Among them, a strain identified as Enterococcus faecium NIAI 157 show ed a clear BLA against the indicator strain, Ent. faecium IFO 13712. The pr oteinaceous nature and antimicrobial activity against closely related speci es strongly indicated that this BLA was a bacteriocin and was designated en terocin ON-157. The bacteriocin activity of this strain was extracellularly produced in the logarithmic growth phase in MRS broth and purified by ultr afiltration, ammonium sulphate precipitation and cation-exchange chromatogr aphy. Purified enterocin ON-157 had a molecular weight of approximately 250 0 Da in SDS-PAGE analysis and was easily inhibited by treatment with alpha- amylase and proteolytic enzymes. Enterocin ON-157 had a bactericidal mode o f action and inhibited the growth of the enterococci, Lactobacillus sake an d Listeria monocytogenes. Enterococcus faecium NIAI 157 harboured two plasm ids, 49.0 kb and 43.7 kb, and a variant missing a larger plasmid by curing with novobiocin lost the bactriocin activity.