Microecology looks for the relationships between microorganisms and their natural environment in definite sites and their physiological and pathological effects. From birth Candida spp. are often but not always detectable in the human gastrointestinal tract. In cases of reduced defense the tract may be a source of infection to the macroorganism. In healthy subjects the incidence of Candida is between 23% and 76% in quantities between 10(2)-10(4) CFU/ml or g dependent on site. Evidence is most frequent in oral cavity and faeces. Tolerance for Candida spp. is different in the stomach and duodenum due to differences in acidity. Changes in the occurrence of Candida spp. are possible depending on age, different diseases and exogenous influences as nutrition, stress and drugs. In an endocrine stress model we found no yeasts in the duodenal juices of 7 subjects before and after stress situation, but a clear decrease of yeasts in the faeces. The formation of metabolic products by Candida is secondary to the whole of microbial fermentation in the human orointestinal tract. Colonizing strains of C. albicans are normally present in small or moderate numbers and only they are regarded as part of the resident gastrointestinal microflora.
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