It was shown the comparative antimicrobial activity of postbiotics isolated from lactic acid bacteria (LAB) strains of genus Enterococcus and Lactobacillus against three broad panelsof human pathogens showed strain-specific inhibitory effects, highlighting their narrower antimicrobial spectrum relative to antibiotics.
Abstract
It was shown the comparative antimicrobial activity of postbiotics (bacteriocins and exopolysaccharides) isolated from lactic acid bacteria (LAB) strains of genus Enterococcus and Lactobacillus against three broad panelsof human pathogens. The antimicrobial activity was assessed in a concentration-dependent manner and compared with that of conventional antibiotics. Selected and purified bacteriocins from strains of
L. rhamnosus
2012 and
E. faecium
KE5, for which an MIC of 5 mg/mL was established against
S. typhimurium
G-38 via the serial dilution method, exhibited the strongest antimicrobial activity across a broad panel of pathogens when tested at this concentration using agar diffusion assays. Postbiotics displayed strain-specific inhibitory effects, highlighting their narrower antimicrobial spectrum relative to antibiotics. It was shown that conventional antibiotics demonstrated broad-spectrum efficacy against susceptible strains but known failures against multidrug-resistant (MDR) isolates. Differences in antimicrobial effects between postbiotics may depend on their interaction with the cell membrane of pathogens. These findings suggest that LAB-derived postbiotics could serve as complementary antimicrobial agents (with antibiotics or another bioactive substance), which may have applications in nutritional and preventive frameworks.
Background: Some lactic acid bacteria are known to synthesize postbiotics, including bacteriocins and exopolysaccharides. Bacteriocins have antimicrobial and anti-inflammatory effect, exopolysaccharides plays an important role in fermented dairy products and can also be beneficial to human health. The present study aimed to evaluate the concentration-dependent antimicrobial activity of postbiotics—bacteriocins and exopolysaccharides produced by probiotic strains of the Enterococcus genus during co-cultivation and interactions in vitro.
Methods: Purification of postbiotics were carried out by gel filtration methodon Sephadex G-50 (exopolysaccharides) and G-25 (bacteriocins). Antimicrobial activity was determined following CLSI and EUCAST.The molecular weights of purified postbiotics were determined using fast protein liquid chromatography (FPLC).
Results: Evaluation of exopolysaccharidesand bacteriocins derived from mixed-strain complex demonstrated a reduction in antimicrobial activity. In vitro assays showed that the combination of exopolysaccharide (Enterococcus genus) with bacteriocins (Lacticaseibacillus rhamnosus 2012 and strains of genus Enterococcus) decreased overall antimicrobial activity by 10% to 64%, depending on the strain originand the properties of their bacteriocins. This finding challenges the assumption of purely additive effects in multi-metabolite postbiotic systems
Conclusion: These findings highlight the importance of considering inter-strain interactions in the co-cultivation of probiotic strains for the development of novel antimicrobial probiotic biopreparations. The antimicrobial efficacy of multi-strain formulations may be influenced by interactions between exopolysaccharides and bacteriocins synthesized during bacterial growth, which may depend on different structure of postbiotics. Obtained data should be taken into account in the design of probiotic-based strategies for the prevention of some infectious diseases
Novelty of the Study: This research provides the first systematic evaluation of the in vitro interactions between purified bacteriocins and exopolysaccharides (EPS) produced specifically by probiotic Enterococcus strains. It identifies a previously underreported antagonistic relationship, demonstrating that the structural interference of high-molecular-weight EPS can reduce the antibacterial efficacy of bacteriocins by 10% to 64%. This finding is critical for the precise design of multi-metabolite postbiotic formulations, challenging the assumption, of purely additive effects in such systems.
Keywords: Postbiotics, Enterococcus, bacteriocins, exopolysaccharide, antimicrobial activity, antagonistic interaction, functional food.
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