Human Microbiota Research − Present and Future −Tomotari Mitsuoka (Emeritus Professor, The University of Tokyo)Characteristic bacterial species inhabit on or in the human body including the skin, mouth, pharynx,stomach, intestine, vagina, urethra, and make up indigenous microbiota. Equilibria exist not only betweenthe indigenous microbiota and the host, but also between the different species within the flora. Many ofthe indigenous bacteria are potential pathogens. If the equilibra are disturbed by certain factors, thepotential pathogens may become involved such so-called “opportunistic infections” as bacteremia,pneumonia, lung abscess, lung gangrene, peritonitis, cholecystitis, cholangitis, liver abscess, diarrhea,enteritis, stomatitis, tonsillitis, brain abscess, meningitis, pyelitis, cystitis, vaginitis, endocarditis,tympanitis, conjunctivitis, soft tissue abscess, etc.(Table). Disturbances of equilibria are seen in suchfactors as administration of antibacterial agents or steroid hormones, surgical operations, stresses,diabetes, overwork, aging, etc.
During the last 5 decades research on intestinal microbiota made rapid progress: 1) Developmentof comprehensive culture method; 2) Establishment of classification and identification of intestinalanaerobic bacteria; 3) Accumulation of micro-ecological evidences; 4) Beneficial and harmful functionof intestinal microbiota in health and disease.
The composition of the intestinal flora can be altered by many factors such as aging, physiological state, drugs, various diseases, diet, stresses, etc. and affect the intestinal metabolism, whichhave a great influence on nutrition, drug efficacy, physiological function, aging, carcinogenesis, immunity, infection and others in the hosts. Thus, it was important to increase beneficial bacteriasuch as bifidobacteria and to suppress harmful bacteria such as clostridia among the intestinalflora for prophylaxis against geriatric diseases including cancers.
Recent advances of research in intestinal microbiota are the background for appearance of functional foods (probiotics, prebiotics, and Biogenics: Figure). They act directly or indirectly throughmodulation of intestinal flora to health of the hosts. Probiotic and prebiotics act on the intestinalmicrobiota and improve the balance of the microbiota by enhancing the growth of beneficial intestinal bacteria and/or suppressing the growth of harmful ones, resulting in scavenging in the intestinal environment. They often induce production of biogenics such as antibacterial substances, immunopotentiators, etc. by the proliferation of beneficial intestinal bacteria. Biogenics include biologically active peptides, including immunopotentiator (biological response modifier:BRM), plant flavonoids, etc. Thus, the functional foods improve stresses, appetite, and absorption, enhance biodefencesuch as immunity and anti-allergy, prevent diseases including diarrhea, constipation, cancer, cholesterolemia, diabetes, etc. and suppress aging, through immunostimulation as well as suppressionof mutagenesis, carcinogenesis, oxidation processes, intestinal putrefaction, and cholesterolemia.
Since the late 1960s molecular biological methods were applied in research on intestinal microbiota. Classification based on genetic relatedness of bacteria were first applied in bacterial taxonomy and has made it possible to provide a more unifying concept of a bacterial species. On thebasis of rRNA homology results or of 16S rRNA oligonucleotid similarity, the establishment of several genera have been proposed. Molecular biological methods have also applied for analyzing micro-biota in both normals and patients. Tools of molecular genetics and molecular biology will be usedto analyze biochemical activities of bacteria in situ in intestinal content and epithelial mucus andhow those activities are regulated at the genetic level, and enhance our understanding of symbioticcross-talk between the biota and the host’s animal tissues.
In future, the high possibility exists, that fundamental foods are used as complementary andalternative medicine agents in both prophylaxis and therapies for the diseases related to immunityand allergy.