Exploring Beneficial Properties of the Bacteriocinogenic Enterococcus faecium ST10Bz Strain Isolated from Boza, a Bulgarian Cereal-Based Beverage

Abstract

The bacteriocin-producing strain Enterococcus faecium ST10Bz, isolated from boza, a Bulgarian cereal-based beverage, exhibited strong activity against Listeria strains, vancomycin-resistant and other Enterococcus strains, but not against most of the other lactic acid bacteria (LAB) strains included in the test panel. Bacteriocin ST10Bz was proven as a stable antimicrobial, even after exposure to various environmental conditions, including varying pH values, temperatures, and commonly used chemicals in industry and laboratory practice. Bacteriocin activity against L. monocytogenes ATCC®15313™ was recorded at 25,600 AU/mL when the producer strain was cultured in MRS broth at 25 °C and 30 °C, and 19,200 AU/mL, when cultured at 37 °C. Additionally, bacteriocin ST10Bz exhibited bactericidal mode of action when added to actively growing cultures of L. monocytogenes ATCC®15313™ and Enterococcus faecalis 200A. E. faecium ST10Bz was susceptible to the antibiotics kanamycin, gentamycin, ampicillin, streptomycin, tylosin, chloramphenicol, clindamycin, tetracycline, and vancomycin; with no evidence for vanA, B, C, D, E, or G genes. PCR analysis of DNA from strain ST10Bz generated positive results for presence of some bacterial adhesion genes, including map, mub and ef-tu, as well as the gamma aminobutyric acid (GABA) production-related gene, gad. Under simulated gastrointestinal conditions in single and co-culture with L. monocytogenes ATCC®15313™ and E. faecalis 200A, E. faecium ST10Bz showed a high survival rate and the ability to reduce the viable numbers of the two test strains.