As early as in the 1930's, Japanese physicians declared that the right balance of intestinal bacteria could prevent disease. At least 500 different types of bacteria make up what is known as the intestinal flora. The beneficial bacteria (Lactic Acid Bacteria) keep the digestive system healthy by limiting the growth and numbers of potential pathogens. Complaints such as persistent diarrhoea, Crohn’s disease, and ulcers caused by Heliobacter pylori, are all associated with a disruption in the normal levels of beneficial bacteria in the intestine. Administering Lactic Acid Bacteria is thought to restore the intestinal flora to optimal levels by allowing beneficial bacteria to attach to the intestinal wall and crowd out harmful bacteria (Parkhurst, 1999).

Recent research has also suggested that the state of the intestinal flora may play a role in the occurrence of colon cancer.

A 1999 study showed evidence that probiotics might have a positive effect in combating this fatal disease (Andersen-Parrado). Furthermore, the study raised speculation that the acidic environment caused by probiotics in the colon disrupts the survival of carcinogenic cells and may decrease the progression of tumours.
The best outcomes of probiotic therapy have been reported in studies investigating the treatment of children with diarrhoea. This is a serious illness in young children because it can cause dehydration severe enough to require hospitalisation. A 2002 issue of the Harvard Health Letter reported on a study comparing traditional treatment with that of probiotic treatment in children hospitalised with serious diarrhoea. The traditional treatment consists of administering an oral hydration solution and the probiotic treatment in this study was an oral hydration solution containing Lactobacillus GG. It was found that patients treated with the solution containing Lactobacillus had a shorter period of illness and a shorter hospital stay. From these studies, it is evident that it is beneficial to incorporate certain microorganisms into our diet.

Bacteriocins

Bacteriocins are anti-microbial peptides that are produced by some strains of Lactic Acid Bacteria, when they grow. These have a bacteriostatic effect on specific target organisms. In contrast to antibiotic compounds, bacteriocins have a high level of specificity, that is, they kill only the target microbes with high selectively.
These anti-microbial peptides are relatively safe and nontoxic in human and livestock use and do not bring about any antibiotic resistance problems. They can be used as bio-preservative and bio-regulator materials. They are now developed as an alternative medicine to replace traditional anti-microbial compounds by utilizing their high target specificity.