Diet is an important factor that determines the composition of bacterial populations in the colonic microbiota, as well as affecting their abilities to carry out many biochemical transformations. Starches that escape digestion in upper gut and non-starch polysaccharides (dietary fibre) are quantitatively the most important substrates for intestinal bacteria. Carbohydrate fermentation is one of thekey events in the large bowel, especially SCFA production. Because the majority of intestinal microorganisms are saccharolytic, carbohydrate metabolism interacts with other biochemical processes mediated by the microflora, such as protein breakdown and amino acid formation, where it has a protective effect against the often toxic products of putrefaction. In many species, the breakdown of complex polysaccharides and the synthesis and activities of substrate uptake systems is controlled by catabolite regulatory mechanisms. The factors that govern fermentation product fermentation are multifactorial, including the anatomy of the colonitself, the types and amounts of food consumed by the host, ecological interactions between different groups of bacteria, individual bacterial strategies for acquiring substrate and their catabolic processes. Substrate availability and bacterial growth rates have been shown to strongly affect fermentation product formation in chemostat studies with Clostridium perfringens, Bacteroides ovatus and Bifidobacterium breve, where high growth rates and high levels of substrate predispose towards the production of electron sink products such as lactate and succinate. Bacterial populations growing in biofilmson the surfaces of digestive residues in the gut lumen were found to be phylogenetically similar to non-adherentcommunities, but were biochemically distinct with respect to enzyme synthesis and fermentation product formation.
In the current intensive live stock industry the gut flora can be disturbed as aresult of several stressors that affect the intestinal tract. New food safety regulations demand to replace antimicrobial additives in poultry feed and still produce healthy poultry. Probiotic micro-organisms like lactic acid bacteria administered with the feed may contribute to a strategy to comply with these demands.Lactobacilli have been shown to stimulate immunity, increase colonisation resistance and increase competitive exclusion. This review highlights some effects of probiotics and their working mechanisms. It is concluded that still more effort should be directed towards the mechanisms behind immune stimulating properties, their contribution to resistance against enteric infections, and the selection of probiotic strains.
This brief overview highlights the antimicrobial substances including bacteriocins produced by lactic acid bacteria, with a particular emphasis on bacteriocin produced by probiotic bacteria, such as Lactobacillus acidophilus and bifidobacteria.
Probiotics are initially defined as food supplements containing live microorganisms which beneficially affect the host by improving intestinal microbial balance. Although the definition has been expanded by other researchers from time to time, in this view, lactic acid bacteria (LAB) are unalterably considered to be the main components of probiotics as they fulfill, in the best course, the requirements targeted by the basic idea of these expanded definitions. It has been believed that periodical supplementation of special cultures of probiotic LAB is helpful to keep the person who consumes it in good health. Recently, the ingestion of LAB as a probiotic has drawn much interest all over the world because of growing health consciousness and concern. A typical example is seen in Japanese society. Well-being is one of the most important matters of concern for Japanese because of the rapid aging of the society. The beneficial image of probiotics has led to an increase in the consumption of fermented milk products in Japan as well as in other countries. Bifidobacteria are often used as dietary supplements or as starter cultures in the production of fermented milk products used as health foods. I have developed the probiotic strain Bifidobacterium longum SBT2928 (BL2928) over a decade for this purpose. This review summarizes the research done to demonstrate the biological functions of BL2928, especially regarding its effect on the host's immune system, on intestinal transit as well as the intestinal microflora composition and metabolism, and specific competitive exclusion of enterotoxigenic Escherichia coli by a novel anti-infectious factor (BIF).
Although the intestinal flora is thought to have a critical role in carcinogenesis, there is little information regarding the role of the human intestinal flora on the effects of dietary and environmental mutagens in vivo. By inoculating germfree animals with feces, the major composition of human flora can be transferred into the ex-germfree animals, i.e. human flora-associated (HFA) animals. The HFA animals provide a stable tool for studying the ecosystem and metabolism of human intestinal flora, though they have some limitations as a model. The capacity of human feces to activate or inactivate mutagens could be transferred into HFA mice and the presence of an intestinal flora was essential for the activity of feces against the mutagens. DNA adduct formation after the administration of dietary and environmental mutagens to mice with different bacterial conditions, including HFA mice, were then analyzed as an in vivo biomarker of cancer risk, and the results indicate that the intestinal flora have an active role in DNA adduct formation. It has also been demonstrated that the role of human intestinal flora is different from that of experimental animals in vivo as well as the metabolic activities against mutagens in vitro. Studies using HFA animals should provide much needed information of relevance to humans regarding the role of intestinal flora in carcinogenesis in vivo. The HFA animals could then contribute to prevention strategies for cancer involving improvement of the intestinal flora.
Soymilk contains raffinose and stachyose, which cause flatulence and n-hexanal and pentanal, which are responsible for bean flavour. The potential of four strains of Bifidobacterium was studied for production of α-galactosidaseand their ability to utilise raffinose and stachyose in reconstituted skim milk and n-hexanal and pentanal in soymilk during fermentation. The potential of raffinose and stachyose for selective enumeration of Bifidobacterium spp. was also studied. All strains possessed α-galactosidase activity, which enabled them to hydrolyse raffinose and stachyose in reconstituted skim milk. n-Hexanal and pentanal in soy milk were metabolised by all four strains of bifidobacteria. Results also indicate that raffinose could be used for selective enumeration of bifidobacteria.
This study was conducted to investigate the effects of bifidobacterial adherence to Caco-2 and MA-104 cell, and of crude peptidoglycan (cPGN) derived from bifidobacteria on Escherichia coli O157: H7 and rotavirus infection in vitro. The results obtained were as follows; at pH 6.6, distribution of cPGN particle size did not show any difference between physical and enzymatic treatment, while average particle size of physical and enzymatic treatment showed 1.26±0.17 and 1.35±0.21, respectively. And then, no differences in the distribution of particle size of bifidobacterial cPGN depending upon Bifidobacterium strains tested were shown. Also, increasing effect of bifidobacterial adherence to Caco-2 cell was shown only to cPGN with enzymatic treatment. As bifidobacterial cPGN concentration increased, adherence ability of bifidobacteria to Caco-2 cell also increased. Nevertheless, no promoting effect was shown to bifidobacteria which possessed low adherence ability, and adherence of E. coli O157: H7 to Caco-2 cell remained unchanged. Subsequently, it was shown that promoting effect of bifidobacterial cPGN on adherence of bifidobacteria to Caco-2 cell reduced adherence percentage of E. coliO157: H7 relatively. In order to investigate the inhibitory effects of bifidobacteria-derived materials on rotavirus infection, effect of bifidobacterial cPGN was assessed by CPE observation and AEC staining method using MA-104 cell. Accordingly, dead cell mass (DCM) and cPGN had positive effectiveness on inhibition of rotavirus infection. Considering adherence ability of Bifidobacterium infantis MAEIL-K9 to MA-104 cell and percentage of rotavirus infection, the higher adherence ability increased, the lower rotavirus infection decreased. Additionally, when Bif. infantis MAEIL-K9 and cPGN were reacted with MA-104 cell simultaneously, adherence percentage of Bif. infantis MAEIL-K9 increased with cPGN added, followed inhibitory effect of bifidobacteria on rotavirus infection also increased. Consequently, even though cPGN derived from bifidobacteria did not show inhibitory effect on E. coliO157: H7, it was proven that adherence of E. coli O157: H7 to Caco-2 cell was relatively inhibited by competition against adherence site, according to increment of adherence percentage of bifidobacteria. Moreover, bifidobacteria-derived cPGN and adherence percentage of bifidobacteria appeared to be protective against human and bovine rotavirus infection. In conclusion, relying upon increment of bifidobacterial viable cell counts, its adherence ability, and adherence-promoting materials to Caco-2 cell, inhibitory effects of bifidobacteria on E. coli O157: H7 and rotavirus infection seemed to be much higher.