Abstract
Recent research into the therapeutic use of living organisms has focused attention on the impact of various disruptive factors (antibiotics, surgery, immunosuppression) and their impact on the host's normal flora. This review covers what is meant by 'normal flora', how the microecology differs by the niche in the body, type of diet, age and health status. In addition, the functions and tools used to investigate normal flora will be explored. The functions of the normal flora include digestion of substrates, production of vitamins, stimulation of cell maturation, stimulation of the immune system, aid in intestinal transit and colonization resistance. A variety of factors can disrupt the normal flora including age, diet, stress, illness and exposure to antibiotics. Research involving microecologic populations is difficult due to the challenge of unraveling the complex dynamics within a usually inaccessible niche, but progress is being made.