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microorganisms inhabiting the intestine of healthy animals and man, generally without harm to the host.
The presence of microbes in the intestine is a symbiotic relationship that developed during the course of evolution. Microbes start to colonize the intestine within hours of the birth of the host, entering primarily with the food. The intestinal flora changes until the host reaches adulthood, when the flora becomes more or less stable. This normal intestinal flora consists of two groups of microorganisms: (1) commensal forms and saprophytes and (2) potentially pathogenic forms.
There are comparatively few microbes in the upper section of the small intestine, since most are destroyed in the stomach by the hydrochloric acid in the gastric juice. Aerobic streptococci (enterococci), lactobacilli, and yeasts are dominant in this section. In the lower sections of the intestine there are more gram-negative bacteria (primarily of Bacillus coli ) and spore-forming bacilli. A gram of feces contains 3–5 X 1011 microbes. There are about 1015 microorganisms in the total intestinal content. Disruption of the species composition and microbe ratios of the intestinal flora by, for example, antibiotics is called dysbacteriosis (dysbiosis). The progress of the digestive processes and the formation of a number of enzymes (for example, cellulase, which decomposes cellulose) and other physiologically active substances not synthesized by the host (certain amino acids, nucleo-tides, and vitamins) depend on the composition and condition of the intestinal flora.
KH. KH. PLANEL’ES