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Degradation of complex carbohydrates by bifidobacteria
Makovská, Marie ; Bunešová, Věra (advisor) ; Švejstil, Roman (referee)
In my bachelor thesis I discuss different strains of bifidobacteria and their ability to utilize different complex carbohydrates as an energy source. For this bachelor thesis were used 112 strains of Bifidobacterium genus which came from different ecological niches. Official collection type and untyped strains were used, along with wild strains, some of which have been isolated by workers and students of the Faculty of Microbiology, Nutrition and Dietetics at the Czech University of Life Sciences. Pure cultures were inoculated into media enriched with different substrates (3 types of starch and Nutriose - resistant dextrin), while tested substrates were always sole carbon sources. Media contained bromcresol red as a pH indicator. A positive sample of the culture, which was able to utilize the substrate, exerted a color change, because of the formation of metabolites (especially acetic acid and lactic acid), which was resulted in lowering the pH.
Further, cultures were tested for ability to degrade starch with so-called plate method. Petri plates contained an agar enriched with starch and tested Bifidobacterium strains were inoculated in preformed holes. After an anaerobic cultivation, coloration by Congo red agent and rinse by NaCl, bright zones around the samples, which prove ability to degrade starch by the bifidobacteria culture, were evaluated.
By the evaluation of the tests has been found that degradation of starch is more frequent for animal strains (which are more species-diverse). Positively respond 59,7 % of total 61 animal strains (20 different species of total 35). Strains isolated from human sources have less capacity of starch degradation. There 26 % of total 42 strains were able to degrade starch. However these positive strains include 8 different species of total 14 tested. From 6 dietary sources of strains just 2 strains (2 different species of 4 tested) were able to degrade starch. One of them was isolated from probiotic product (drops) and the second one was isolated from airag (Mongolian traditional fermented drink, which is made from the milk of mares). All three strains, which were isolated from sewage, can degrade starch (each of them was different species).
The results suggest that some substrate preference of Bifidobacterium strains depends of their habitat.
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