Gastrointestinal tract microflora importance

The gastrointestinal (GI) microflora plays an important role in the health status of people and animals. The GI tract represents a much larger contact area with the environment, compared to the 2 m2 skin surface of our body (van Dijk 1997). The mucosal surface of the small intestine is increased by forming folds, intestinal villi, and the formation of microvilli in the enterocyte resorptive luminal membrane. The resulting surface of GI system is calculated to be 150-200m2, therefore it provides enough space for the interactions related to digestion and for the adhesion to the mucosal wall. 

The primary fate of dietary fibers is digestion and catabolism by the gut microflora to short-chain fatty acids and carbon dioxide. The major products of this microbial metabolism — acetic, propionic, and butyric acid — are important sources of energy for ruminants (sheep, cows). Dietary fiber is retained in a chamber of their gastrointestinal tracts, called the rumen, where it is converted to short-chain fatty acids by the gut microflora. The fatty acids produced may supply 35-75% of the energy requirement of the ruminant. 

The enzymes responsible for reduction may be located in both the microsomal fraction and the soluble cell fraction. Reductases in the microflora present in the gastrointestinal tract may also have an important role in the reduction of xenobiotics. There are a number of different reductases which can catalyse the reduction of azo and nitro compounds. Thus, in the microsomal fraction, cytochromes P-450 and possibly a flavoprotein are capable of reductase activity. NADPH is required, but the reaction is inhibited by oxygen. FAD alone may also catalyse reduction by acting as an electron donor. 

The ability of the probiotic strain to persist in the gut has been identified as one important prerequisite of probiotic efficacy. Indeed, a number of probiotic products claim that their strains colonize the human gastrointestinal tract. However, it is more likely that after cessation of probiotic feeding, the vast majority of probiotic strains fall below detection. This is not imexpected since the human gut microflora provides a robust barrier to the establishment of exogenous micro-organisms. 

Roberton, A.M., and Corfield, A.P. Mucin degradation and its significance in inflammatory conditions of the gastrointestinal tract. In Medical Importance of the Normal Microflora (Tannock, G.W., ed.) (1998) Kluwer Academic Publishers, Dordrecht, Boston, London, pp. 

Intestinal microflora are an essential component of human physiology because they act as a barrier against colonization of the gastrointestinal tract by pathogenic bacteria. They also play an important role in the digestion of food and in the metabolism of xenobiotics. 

Bacteria within the gastrointestinal tract perform a wide variety of biochemical reactions (77). Since the lower part of the gastrointestinal tract is anaerobic, the biochemical reactions performed by intestinal microflora are usually reductive and hydrolytic in nature. Nitro-PAH metabolism by intestinal microflora has been demonstrated both in vitro and in vivo (Table 1,2). It is well established that the nitroreductases of intestinal microflora are responsible for the metabolism and bioactivation of nitro-PAHs. However, it should be noted that the intestinal microflora are not separate from the host metabolic processes and that synergistic metabolic interactions between enzymes of the gut mucosa, hepatic tissue and microflora are important in the metabolic activation of nitro-PAHs. El-Bayoumy et al. (25) and Kinouchi et al. (45) demonstrated that the predominant metabolites formed from 1-nitropyrene-treated germ-free animals (intestinal microflora were absent) were primary ring-hydroxylated derivatives of... 

---