出版社：Japanese Society of Nutrition and Food Science
摘要：The indigenous microorganisms resident in the digestive tract of men and animals have been studied extensively in recent years. Investigations with germfree or gnotobiotic animals have demonstrated the important influence that the intestinal microflora has on the metabolism of the host and of a wide variety of substances within the intestinal lumen, and on intestinal morphology and function. Germfree animals generally have the lower metabolic rate than conventional animals. Intestinal bile acids are higher in total concentration, differed in composition, and remain totally conjugated in germfree animals. Microbial modification of bile salts becomes important in various absorptive activity. It is recognised that the intestinal microbial products useful for the host are amino acids, organic acids, vitamins and gases, etc. Of vitamins, the ability of intestinal microorganisms to manufacture thiamine, riboflavin, pyridoxine, niacin, pantothenic acid, vitamin B12, folic acid, biotin and vitamin K is well established. On the other hand, the toxic substances, for example, ammonia, hydrogen sulfide, amines, phenols or hydroxy fatty acids, are also produced by the intestinal microorganisms. Morphological differences of the intestine in germfree animals include cecum enlargement in rodents, lower amount of lamina propria, reduced mucosal surface area, and lower rate of intestinal mucosal cell renewal. The absence of a intestinal microflora produces increase in the absorption of tryptophan, methionine, palmitic and stearic acids, calcium, magnesium, phosphorus, iron, and thiamine. The rates of absorption of oleic and linoleic acids, sodium, pottasium, and vitamin B12 are less in germfree animals than in conventional animals or similar in both groups, but the capacity to absorb xylose during the 6 hours following intragastric administration appears to be slightly greater in conventional animals. The normal microbial flora contributes to the defence of the host by virtue of its competition of invading microorganisms. Recent studies have confirmed that intestinal emptying is significantly more rapid in animals harboring a conventional flora than in germfree animals. This effect undoubtedly constitutes important direct contributions of the normal intestinal microflora to host defense.
