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Influence of some medicinal fungi and other prebiotics on growth and metabolism of probiotic bacteria
Husová, Martina ; Bendová, Agáta (referee) ; Márová, Ivana (advisor)
The bachelor thesis deals with the influence of medicinal mushrooms and other prebiotics on the growth and biological activity of probiotic bacteria. Selected genera of lactic acid bacteria Bifidobacterium and Lactobacillus can produce antimicrobial substances bacteriocins and their production depends on cultivation conditions and available nutrient sources. The theoretical review describes and characterizes probiotic bacteria, their metabolism and importance for human health. Similarly, the theoretical section focuses on prebiotics and their selected representatives, which are four species of medicinal fungi, the microscopic algae Chlorella, resistant starch, the cell biomass of the yeast Saccharomyces cerevisiae and dietary supplements such as inulin and psyllium. In the experimental part, extracts were prepared from these prebiotics by three different methods - boiling, macerating and hydrolysis. The obtained extracts were characterized in terms of macronutrient content such as carbohydrates and proteins. Based on the growth of four species of lactic acid bacteria cultured in standard medium and their production of antimicrobial substances, a strain of B. bifidum was selected for cultivation in the presence of prebiotic extracts. After determining the increase in probiotic biomass in the prebiotic extracts, the cultures were centrifuged, and the protein content of the bacterial supernatant was determined. The lactic acid content of the lyophilized probiotic extracts was determined by high-performance liquid chromatography, and finally, the antimicrobial activity was determined by broth dilution method and resazurin viability assay. The results of the antimicrobial tests were compared with the antimicrobial activity of lactic acid at the same concentration as that contained in the probiotic extracts. For the highest macronutrient content of the prebiotic extracts, extraction by boiling was the most suitable method. For insoluble polysaccharides such as resistant starch, hydrolysis might be a better option, but this requires subsequent treatment of the extract to provide suitable conditions for cultivation. The boiled extracts were the best for the growth of probiotic bacteria as well as their production of antimicrobial substances. The highest concentrations of protein and lactic acid were measured in these samples. The likely presence of bacteriocins was confirmed in all culture types. Almost all probiotic extracts showed antimicrobial activity against Staphylococcus epidermidis and Escherichia coli. The likely presence of bacteriocins was confirmed by the broth dilution method, for example in extracts containing chlorella algae or S. cerevisiae yeast, because these extracts were antimicrobial at lower concentrations than the lactic acid present.
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Production and application of antimicrobial substances produced by lactic acid bacteria
Utíkalová, Kristýna ; Dzurická, Lucia (referee) ; Márová, Ivana (advisor)
The bachelor’s thesis deals with the production of antimicrobial substances by selected lactic acid bacteria of the genera Lactobacillus, Pediococcus and Bifidobacterium, in which the production of bacteriocins was assumed based on the conducted research. Bacteriocins are peptide-based antimicrobial substances with the potential to be widely used primarily as biopreservatives in the food industry. The theoretical part of the bachelor’s thesis focuses on antimicrobial substances produced by probiotic bacteria with a further concentration on bacteriocins produced by selected bacterial species and their current research and application in the industry. In the experimental part, the antimicrobial activity of prepared isolates from probiotic bacteria was tested on selected gram-negative and gram-positive bacteria. Specifically, this was done by the agar diffusion method, the broth dilution method and the cell viability test using resazurin. The amount of lactic acid and acetic acid in the individual isolates was determined using high performance reverse-phase liquid chromatography, which made it possible to further discuss their influence on the antimicrobial activity of the isolates. Strong antimicrobial activity against indicator bacteria was found in all isolates. For some isolates, it was higher than the antimicrobial activity of lactic acid itself together with its concentration which is found in the isolate according to the measurements. That is a significant stimulus for further research of these probiotic isolates, especially the L. acidophilus and L. plantarum isolates. For example, it was found that the tested isolate from L. acidophilus showed an inhibitory activity against S. epidermidis of 90,76 % and 81,62 % against E. coli at a concentration of 20,47 mg/ml. The isolate from L. acidophilus was subsequently applied to plant packaging with the potential of usage in the food industry, and the inhibitory activity of this isolate against contaminating microorganisms was observed.
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