Abstract
Enterococcus faecium CN-25 was isolated from a traditionally Thai fermented fish roe, som-kai-pla, and was found to possess enterocin A and B genes. Among the 30 microorganisms tested, the produced bacteriocin exhibited antagonistic activity against Listeria monocytogenes TISTR 1327. The bacterium maximally produced bacteriocin at a concentration of 1828 AU/ml at the beginning of the stationary phase (at 18 h) in the inexpensive rice bran medium. The antilisterial activity of the compound was not affected by heating at 60–100 °C for up to 30 min. High antilisterial activity remained at pH 2. Partially purified CN-25 bacteriocin derived from E. faecium CN-25 completely inhibited the growth of L. monocytogenes at the minimum concentration of 2.38 μg/ml. The compound had no effect on the efflux of ATP from L. monocytogenes but triggered the intracellular hydrolysis of ATP, as evidenced by a decrease in the luminescence of total ATP. The bacteriocin also depleted the transmembrane electrical potential (ΔΨ) but had no effect on the transmembrane pH gradient (ΔpH). Therefore, the partially purified CN-25 peptide may be useful for improving the product safety of fermented fish products.
•Enterococcus faecium CN-25 was isolated from Thai fermented fish roe, som kai pla.•It produced enterocin A and B with strong inhibition against L. monocytogenes.•The highest bacteriocin production was attained at the stationary phase.•The bacteriocin remained active over a wide pH range of 2–12.•The bacteriocin only depleted the transmembrane electrical potential (ΔΨ).