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Normal Microbiota of the Human Body Introduction Symbiosis is the living together in close physical association of two or more different organisms Ectosymbiosis - organisms remain outside each other Endosymbiosis - one organism is found within the other Types of Symbiosis, Functions, and Examples Commensalism - the microorganism (commensal) benefits, while the host is neither harmed nor helped Distribution of the Normal Microbiota of the Human Body Reasons to acquire knowledge of normal human microbiota and its distribution It provides greater insight into possible infections resulting from injury to these areas It gives perspective on the possible sources and significance of microorganisms isolated from an infection site It increases understanding of the causes and consequences of overgrowth of microorganisms normally absent from a specific body site It aids awareness of the role these indigenous microorganisms play in stimulating the immune response that provides protection against potential pathogens Skin Resident microbiota multiply on or in the skin
Transient microbiota are found on the skin for a short time and do not multiply there; they usually die in a few hours
Nose and nasopharynx Nose - just inside the nares;
Nasopharynx - above the level of the soft palate;
Oropharynx - between the soft palate and upper edge of the epiglottis; houses many different species Respiratory tract - no normal microbiota due to mucociliary blanket, the enzyme lysozyme in mucus, and the phagocytic action of alveolar macrophages Oral cavity (mouth) - contains those organisms that survive mechanical removal by adhering to gums (anaerobes) and teeth (aerobes); organisms contribute to the formation of dental plaque, dental caries, gingivitis, and periodontal disease Eye - aerobic commensals are found on the conjunctiva External ear - resembles microbiota of the skin with some fungi Stomach - most microorganisms are killed by acidic conditions unless they pass through very quickly; the number of microorganisms present increases immediately after a meal, but decreases quickly Small intestine Duodenum - few microorganisms present because of stomach acidity and inhibitory action of bile and pancreatic secretions Jejunum - Enterococcus fecalis, diphtheroids, lactobacilli, and Candida albicans Ileum - microbiota resemble that of the colon as the pH becomes more alkaline Large intestine (colon) - largest microbial population of the body Over 300 different species have been isolated from human feces Most are anaerobes or facultative organisms growing anaerobically Ratio of anaerobes to facultatives is approximately 300:1 They are excreted by peristalsis, segmentation, desquamation, and movement of mucus They are replaced rapidly because of their high reproductive rate This is a self-balancing (self-regulating) microbial ecology The balance may change with: stress, altitude, starvation, diet, parasite infection, diarrhea, use of antibiotics or probiotics (microorganisms orally administered that promote health) Genitourinary tract Kidneys, ureter, and bladder are normally free of microorganisms Males - a few microorganisms are found in distal portions of the urethra Females - complex microbiota in a state of flux due to menstrual cycle; Döderlein’s bacilli are primarily Lactobacillus acidophilus that forms lactic acid and thereby maintains the pH of the vagina and cervical os between 4.4 and 4.6 |