Media Optimization for Bacteriocin Production by Enterococcus faecium Strains Isolated from Traditional Korean Soybean Paste

Bacteriocinogenic Enterococcus faecium ST651ea, ST7119ea, and ST7319ea, were previously isolated from traditional Korean fermented soybean paste and identified by 16S rRNA sequencing and appropriate biochemical and physiological tests. Growth conditions for bacteriocin production by E. faecium ST651ea, ST7119ea, and ST7319ea were optimized regarding the inhibition of vancomycin-resistant E. faecium VRE19 of clinical origin, and Listeria monocytogenes ATCC15313 as a reference strain. When cultured in MRS broth for 24 h, E. faecium ST651ea, ST7119ea and ST7319ea produced 3200 AU/ml, 6400 AU/ml, and 6400 AU/ml, respectively, at 37oC, and 1600 AU/ml, 3200 AU/ml and 3200 AU/ml, respectively, at 30oC against E. faecium VRE19. MRS medium compositions were modified based on inclusion, exclusion, and/or replacement of components for optimizing the production of bacteriocins by these strains. Bacteriocins produced by E. faecium ST651ea, ST7119ea, and ST7319ea showed higher activity at 37oC after 15h with 20 g/l galactose replacing D-glucose and in setups containing organic nitrogen sources of only 10 g yeast extract/l and 15 g peptone/l in modified MRS. The bacteriocin produced by E. faecium ST651ea yielded 6400 AU/ml and 25600 AU/ml activity against E. faecium VRE19 and L. monocytogenes ATCC15313, respectively. For E. faecium ST7119ea results were 12800 AU/ml and 51200 AU/ml and for E. faecium ST7319ea were 12800 AU/ml and 51200 AU/ml against E. faecium VRE19 and L. monocytogenes ATCC15313, respectively. Based on the type and availability of different carbohydrates and organic nitrogen sources production of bacteriocins by E. faecium ST651ea, ST7119ea, and ST7319ea was reduced by up to 50%.