Microecology of the gastrointestinal tract in relation to lactic acid bacteria

The distal small bowel and the large bowel of humans, even in health, are inhabited by a complex collection of microbes (mostly bacteria) knows as the normal microflora. Gram-positive, lactic acid-producing bacteria are represented in this collection (bifidobacteria, lactobacilli, enterococci, eubacteria, peptostreptococci). The influence of the normal microflora as a whole on the host is well known from studies comparing germfree and conventional animals. More recently, using an unique experimental animal system (loctobacillus-free mice), lactobacilli have shown to to influence markedly the biochemistry of the intestinal tract (azoreductase, beta-glucuronidase, bile salt hydrolase, proportions of unconjugated/conjugated bile acids). The effect of the consumption of lactic acid-producing bacteria on the normal microflora and the intestinal milieu of humans is therefore of interest. Detailed analysis of the composition, at the level of bacterial strains, of the normal microflora should be possible using DNA probes and ribotyping. These studies are necessary to provide a basis for the study of the effects of ingested lactic acid bacteria on the large bowel ecosystem, and for the derivation and use of genetically modified bacterial that will have a desirable impact on human health.