Normally you have between four and seven pounds of bacteria in your colon. Normal and well-balanced bacteria have many beneficial functions.
Beneficial bacteria do the following:
Produce vitamins like folic acid and B12.
Nourish the lining of the colon by feeding on vegetable fiber and producing butyric acid. Adequate butyric acid levels reduce the chances for colon cancer.
Inhibit harmful bacteria.
Break down toxins.

Other bacteria and yeast normally exist, but in smaller numbers. Think of the GI tract as an ecosystem, with a balance between beneficial and not-so-beneficial microorganisms. When the ecosystem is out of balance, your health can be adversely affected.

Harmful microorganisms do the following:
Inhibit normal bacteria, creating deficiencies of nutrients and other problems.
Produce toxins. Harmful bacteria create toxins and inhibit normal bacteria from detoxifying the bowel. Toxins can burden the liver and affect every function in the body.
Hydrogenate polyunsaturated fatty acids.
Irritate the lining of the intestine, increasing intestinal permeability (leaky gut).
According to research published in the Lancet (April 7, 2001;357:1076-1079), if an expectant mother takes probiotics (“good” bacteria), it reduces the chance of allergies developing in her child. Researchers in Finland used Lactobacillus GG (Lactobacillus rhamnosus), a probiotic, in an attempt to prevent allergies in at-risk infants. Allergy experts say this offers the first good evidence that harmless bacteria can train infants' immune systems.

The infants in the study were determined to be “at risk” because a parent or sibling suffered from allergies. Researchers gave a group of pregnant women a probiotic capsules every day for a few weeks before their due dates. For 6 months after delivery, women who breast-fed continued on the probiotics, while bottle-fed infants were given the treatment directly.

By the age of 2 years, 35% of the children had developed allergic eczema. The children who had received probiotics, however, were half as likely to develop the skin condition.
One hypothesis that explains the increase in allergies worldwide is that our surroundings are increasingly sterile. Some scientists believe that when babies are exposed to germs, their immune systems are steered toward infection-fighting mode and are less likely to overreact to benign substances. Support for this idea comes from studies showing that infants who have more colds and other infections have lower asthma rates later in life.
Documented research has indicated important benefits associated with the use of probiotic bacteria and prebiotic substances. BioDoph-7 Plus was shown to be immuno-modulating by virtue of both the up-regulation of IL-10 production by dendritic cells and the decreased production of interferon-gamma by T-cells. Also noted was a diminished pro-inflammatory effect via a decrease in the lipopolysaccharide production of IL-12 .