The intestinal microbiota is composed of hundreds of species in tens of genera of facultative and anaerobic members of the domainsBacteria and Archaea. Its population exceeds 1× 1014microbial cells. Its mass is one-half that of intestinal content. It influences many physiological and immunological properties of its animal host. This knowledge supports two concepts: 1. the microbiota is an organ of the body essential for survival of man in the natural world, and 2. humans are composites of eukaryotic animal cells and bacterial and archeal members of the biota. These concepts have important implications for research during the 21st Century on human biology and evolution, advancing health, and diagnosis and treatment of disease. Much of that research will be pursued with the technologies of molecular biology and genetics. This review concerns how such technologies might be used to advance our capacities to enhance beneficial influences and minimize harmful effects of the biota.
Fluorescentin situhybridization (FISH) with 16S rRNA targeted oligonucleotides was used in combination with automated microscopy to determine the quantitative composition of the bacterial microflora in faeces of human volunteers. The percentage bifidobacteria andBacteroideswas determined in faecal samples of different age groups (12-20 d breast-fed, 1-3 yr, 18-52 yr, > 75 yr). The percentage bifidobacteria was 72.8, 10.0, 4.0 and 9.2%, respectively. The percentageBacteroideswas 1.3, 24.9, 20.6 and 5.9%, respectively. There are large individual differences especially in adults and even more in elderly. Comparison of the adult age groups in China and the Netherlands shows no significant differences in the percentage bifidobacteria andBacteroides. However the percentage bacteria belonging to the Clostridium coccoides-Eubacterium rectale group was significantly higher in samples from China (31.4%) than in those from the Netherlands (19.9%). Individual differences were large. The effect of oral treatment with metronidazole on the bacterial composition in faecal samples of one volunteer was investigated with several probes. There is a 3-fold decrease in the total number of bacteria and the results show that there is a large increase of lactobacilli-enterococci and an increase of bifidobacteria.Bacteroidesremains unaffected. The results show that automated FISH is an excellent tool to study intestinal bacteriology in response to modulation.
Some of the lactic acid bacteria (LAB) have been considered to contribute to human health and are used in foods and pharmaceutical products as probiotics. Basic studies on the specific effects of these bacteria and their mechanisms of action are indispensable to the verification of their effectiveness. The development of molecular biological techniques plays an important role in the advancement of these studies.Lactobacillus caseistrain Shirota is a lactic acid bacterium isolated from the human intestine and has been used industrially as a probiotic strain, whose beneficial effects on humans and animals, including an immunomodulatory function, are well documented. This report summarizes the developmental situation of genetic manipulation inL. caseistrain Shirota as follows: 1) transformation and plasmid vectors, 2) a system using an integration-excision vector to maintain desired sequences safely and stably on its chromosome, and 3) experimental display of a chimeric protein on the cell surface of the strain Shirota.
Dietary modulation of the human gut microbiota is a topical area of nutritional sciences. This is driven by the fact that the gastrointestinal tract, particularly the colon, is very heavily populated. Undoubtedly, certain gut species are pathogenic and may be involved in the onset of acute and chronic disorder. However, most bacteria in the gut are benign, with the possibility that some groups are beneficial. Bifidobacteria and lactobacilli are thought to belong to this latter category and are common targets for dietary intervention that improves health. Dietary modulation of the human gut microflora by functional foods such as probiotics and prebiotics is designed to improve human health. A probiotic is a live microbial feed supplement, whereas a prebiotic is a non viable food ingredient selectively metabolised by intestinal bacterial species seen as beneficial. Examples of probiotics are lactobacilli and bifidobacteria, given in fermented milks or as lyophilised forms. Fructo-oligosaccharides, lactulose and galacto-oligosaccharides are all popular prebiotics in Europe. These have been shownin vivoto stimulate numbers of bifidobacteria in faecal samples. Many more types exist in Japan. Bifidobacteria and lactobacilli are thought to contribute many health promoting benefits towards the host. These include increased resistance to pathogenic bacteria, lowering blood ammonia, increased stimulation of the immune response and a reduction in the risk of cancer. New functional food developments are set, more than ever, to exploit probiotics and prebiotics. However, it is important that their use is underpinned by robust scientific principles and technologies.
The immune system at birth is not adapted for postnatal life in several respects and the postnatal maturation of the immune system is characterised by the development of a balanced Th1/Th2 immunity. The efficiency and kinetics of this process is slower in atopic children. According to “hygiene hypothesis, ” modern living is associated with too little microbial stimulation early in life. This lack of stimulation of the immune system would in turn result in deficient down-regulation of immune responses to those ubiquitous allergens that the individual encounters early in life. It is likely that the primary signal for such maturation during infancy and early childhood is provided not by pathogens, but by stimulation from the commensal microbial flora, as the gut flora is the quantitatively most important source of microbial stimulation. Differences in the composition of the gut flora are demonstrable very early in life and even before the development of any clinical manifestations of atopy. As the microbial flora is driving the maturation of the immune system, changes in its composition, as a consequence of an altered lifestyle and diet in industrialised societies, my play a role for the higher prevalence of allergy. Clinical trials lend support to the concept that the intestinalmicroflora may have an important role for the immune regulation to allergens and that certain probiotic strains could be used for the treatment of allergy, or even the prevention of disease.
The influence of bile salts on theβ-glucosidase activity ofBacteroides fragiliswas investigated. Theβ-glucosidase is one of the cancer-associated bacterial enzymes. Theβ-glucosidase activity of intact cells and of sonicated cells ofB. fragiliswas higher in the buffer with sodium deoxycholate than in the buffer with sodium cholate or without bile salts. These findings suggest that the presence of bile salts, particularly deoxycholate, links to increase the β-glucosidase activity ofB. fragilisin the large intestine.