Gastrointestinal Microflora in Mammalian Nutrition

Abstract

A mammal is a complex organism consisting of eukaryotic animal cells and eukaryotic and prokaryotic microbial cells. Most of the microorganisms reside in communities in the gastrointestinal tract. These gastrointestinal microfloras are known to serve nutritional functions in ruminants, pseudoruminants, and monogastric mammals with only modest or no foregut fermentations but with extensive hindgut fermentations in blind cecal pouches. In adult animals, the microflora hydrolyzes exogenous (dietary) and endogenous polymers, and provides the adult with all or at least a significant proportion of its carbon, energy, vitamins, and macromolecular building blocks. The flora also functions as a conservator of nitrogen that would otherwise be excreted as urea. In exchange, the flora competes directly with the host tissues for nutrients ingested in the diet, and also competes indirectly by somewhat repressing the absorptive capacities of the animal tissues. When the synergism is in balance, the animal tissues and the microflora operate in harmony for the health and nutritional welfare of the host as a whole. The system may be unbalanced by antibacterial drugs that destroy the microflora and by diseases of the animal tissues that destroy the controls regulating where indigenous communities localize in the tract, their microbial composition, and their biochemical activities. At such times, the nutrition of the animal tissues can be adversely affected to the extreme. Humans living in developed and developing countries have extensive microfloras in their hindguts. Humans living in developing countries may also have extensive microfloras in their small bowels. Those floras may function in nutrition of the animal tissues of man much the same as do floras in similar locations in the gastrointestinal tracts of mammals other than man. However, animals of some species other than human gain much of the nutritional benefit from their microflora through the practice of coprophagy. Since adult humans do not normally practice coprophagy, any nutritional benefit from the microflora depends upon the capacity of the bowel mucosa, principally that of the large bowel, to absorb bacterial products, e.g. short-chain volatile fatty acids. Such absorption undoubtedly occurs, but is surely not a major source of carbon and energy for the animal tissues of man.

Determination of bacterial amino acid contribution to ileal digesta from pigs using ³⁵S and DAPA marker techniques

“…Until recently, bacteria content and activity proximal to the large intestine of the pig had been considered to be of little importance in nutritional terms (Hungate, 1984;Savage, 1986). Hovewer, the iclusion of subtherapeutic levels of antibiotics in diets has been shown to improve growth performance (Yen et al, 1987) and reduce intestinal bacterial ammonia production (Yen et al, 1990) in swine.…”

Microbial regulation of intestinal radiosensitivity

“…These gnotobiotic models have revealed that the microbiota facilitates the breakdown of otherwise indigestible polysaccharide components of our diet (4,5), regulates storage of calories extracted from the diet in adipocytes (3), metabolizes xenobiotics, including carcinogens (6, 7), modulates intestinal epithelial cell turnover (8)(9)(10)(11), and educates the immune system (12,13). The microbiota also collaborates with the host to regulate a number of aspects of postnatal gut development, including the assembly of the extensive network of capillaries in the mesenchymal cores of mouse small intestinal villi (14).…”

Surface Properties of Lactobacillus Strains of Human Origin

“…This strongly suggests that lactobacilli may use mechanisms similar to those of pathogenic bacteria when colonizing mucosal surfaces. It is postulated that lactobacilli can adhere because of the presence of surface structures containing teichoic and lipoteichic acids linked to the cell wall peptidoglycan (15). Protein structures resembling the fuzzy layer extruding from the cell wall surfaces were also found.…”