Characterization and safety evaluation of two beneficial, enterocin-producing Enterococcus faecium strains isolated from kimchi, a Korean fermented cabbage

Enterococcus faecium ST20Kc and ST41Kc were isolated from kimchi, a traditional Korean fermented cabbage. Bacteriocins produced by both strains exhibited strong activity against Listeria monocytogenes and various Enterococcus spp., including 30 vancomycin-resistant enterococcal strains, but not against other lactic acid bacteria (LAB) on the evaluated test panel. The antimicrobials produced by the strains were found to be proteinaceous and stable even after exposure to varying pH, temperature, and chemicals used in the industry and laboratory processes. Antimicrobial activity of both strains was evaluated as bactericidal against exponentially growing cultures of L. monocytogenes ATCC (R) 15313TM and Enterococcus faecalis 200A. Based on tricine-SDSPAGE, the molecular weights of the bacteriocins produced by the strains were between 4 and 6 kDa. Additionally, both strains were susceptible to antibiotics, including vancomycin, kanamycin, gentamycin, ampicillin, streptomycin, tylosin, chloramphenicol, clindamycin, and tetracycline. Adhesion genes, map, mub, and EF-Tu, were also detected in the genomes of both strains. With gastrointestinal stress induction, both strains showed high individual survival rates, and capability to reduce viable counts of L. monocytogenes ATCC (R) 15313TM and Enterococcus faecalis 200A in mixed cultures. Based on the metabolomics analysis, both strains were found to produce additional antimicrobial compounds, particularly, lactic acid, phenyllactic acid, and phenethylamine, which can be potentially involved in the antimicrobial interaction with pathogenic microorganisms.

Automated summary

Enterococcus faecium ST20Kc and ST41Kc isolated from kimchi produce bacteriocins with strong activity against Listeria monocytogenes and various Enterococcus spp. The antimicrobials are proteinaceous and stable, with a bactericidal effect on targeted bacterial strains. Both strains are susceptible to antibiotics and potentially produce additional antimicrobial compounds with metabolomics analysis.