Twenty types make up three-quarters of the total and are present in large amounts. The two strains of bacteria recognized as most important to health are lactobacilli and bifidobacteria. It is now known that where antibiotics are concerned, it is possible to have too much of a good thing. Harmful bacteria are shrewd and wily organisms, and over time will mutate until they become resistant to the particular strain of antibiotics which formerly kept them under control. While antibiotics mow down every organism in their path, probiotics support the growth of good, healthy probiotic bacteria, which then can not only fight but actually prevent the growth of harmful microorganisms, whether old, new, or mutated.
Probiotics can also stimulate the immune system's production of white blood cells.
In healthful quantities, they can crowd out the offending pathogens or cover the areas of the intestinal walls to which the pathogens are fond of attaching. This crowding or starving out process is known as competitive exclusion. Some probiotic bacteria produce lactase, an enzyme which helps alleviate symptoms of lactose intolerance. Most, including l. Fiber helps probiotics to thrive.