Abstract
Three out of one hundred eighty putative LAB isolates from Korean traditional fermented soybean paste were identified to be unique and bacteriocinogenic strains. Based on phenotypic and 16S rRNA sequencing analysis, selected strains were identified as Enterococcus faecium ST651ea, E. faecium ST7119ea and E. faecium ST7319ea. The bacteriocinogenic properties of the studied strains were evaluated against Listeria monocytogenes ATCC15313, Listeria innocua ATCC33090 and vancomycin-resistant E. faecium VRE19 of clinical origin. The strains E. faecium ST651ea, ST7119ea and ST7319ea expressed bacteriocins with an activity of 12,800 AU/mL, 25,600 AU/mL and 25,600 AU/mL, respectively, recorded against L. monocytogenes ATCC15131. According to the PCR-based screening of bacteriocin-related genes, which was further confirmed through amplicon sequencing, showed that strain E. faecium ST651ea carries entB and entP genes, whereas both E. faecium ST7119ea and ST7319ea strains harbor entA and entB genes. The molecular size of expressed bacteriocins was estimated by tricine-SDS-PAGE showing an approximative protein size of 4.5 kDa. The assessment of the spectrum of activity of bacteriocins ST651ea, ST7119ea and ST7319ea showed strong activity against most of clinical VRE isolates, majority of other Enterococcus spp. and Listeria spp. Bacteriocins ST651ea, ST7119ea and ST7319ea were partially purified by combination of 60% ammonium sulfate precipitation and hydrophobic chromatography on the SepPakC18 column. Challenge test with semi-purified (60% 2-propanol fraction) bacteriocins resulted in a significant reduction of viable cells for all test organisms. Thus, indicating that all the bacteriocins evaluated can be used as potential biocontrol in food and feed industries as well as an alternative treatment for VRE-related infections in both veterinary and clinical settings.
Highlights
Thereby, this study focuses on the evaluation, partial characterization and applications of Enterococcus faecium strains and their bacteriocins as a potential biocontrol agent against food-borne pathogen L. monocytogenes and its indicator organism L. innocua, along with vancomycin-resistant Enterococcus, a clinically significant emerging pathogen
The 16S rRNA sequencing analysis showed that the evaluated strains belong to the Enterococcus faecium species and were designated as strains E. faecium ST651ea, E. faecium
It was postulated that the presence of various bacteriocinogenic enterococci in these types of fermented food products acts as an additional hurdle against spoilage microorganisms
Summary
Even though lactic acid bacteria (LAB) are generally known to be fastidious microorganisms, Enterococcus spp., a LAB, has been associated with a wider ecological distribution relative to the other members of the LAB due to their ability to survive in a vast range of pH and temperature and their ability to metabolize varieties of carbohydrates Their applications as starter cultures and probiotics for some fermented food and feed products [1,2,3], and their emerging significant role in the clinical and veterinary sectors as commensals and opportunistic pathogens- in nosocomial infections such as endocarditis, bacteremia and other related infections [4,5,6,7] have highlighted their importance, may it be a boon or a bane, in the food manufacturing industries, veterinary and clinical settings. The majority of the known bacteriocins produced by enterococci are classified under the Class
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