Enterococcus faecium LM-2, a multi-bacteriocinogenic strain naturally occurring in “Byaslag”, a traditional cheese of Inner Mongolia in China

Abstract

A bacteriocin-producing strain LM-2 was isolated from “Byaslag”, a traditional cheese in Inner Mongolia of China, and identified as Enterococcus faecium. The strain produced the maximum activity of enterocin (5120 AU ml −1) in MRS medium in the mid-stationary phase of growth (i.e. after 30 h at 37 °C). Purified enterocin LM-2 was obtained by using a two-step procedure consisting of ammonium sulfate precipitation and cation exchange chromatography. Tricine–SDS–PAGE of the purified enteriocin LM-2 contained two active protein bands between 3.5 and 6.4 kDa. It showed a broad spectrum of activity against most of the tested strains in the genera Listeria, Staphylococcus, Bacillus, Clostridium, Salmonella and Pseudomonas. All Listeria strains tested, including L. monocytogenes, were highly sensitive to this bacteriocin. The inhibitory activity of enterocin LM-2 against L. monocytogenes was bactericidal without concomitant cell growth, and the highest level of adsorption (87.5%) to the surface of L. monocytogenes 54002 cells was founded at pH 6.0. This strong inhibitory activity against L. monocytogenes, coupled with its broad pH-resistance and heat-stability indicated its potential use as a food preservative to enhance the safety of fermented foods. The presence of enterocin P and L50-like structural genes in E. faecium LM-2 was established by PCR and direct sequencing, which indicated strain LM-2 may be a new multi-bacteriocin producer strain.