Lactobacillus acidophilus is a probiotic bacterium that specifically inhabits the small intestine. Studies suggest that some strains of Lactobacillus acidophilus may help control intestinal infections (and therefore help reduce the onset of diarrhea) and improve digestion. Studies also show acidophilus may cause an inhibitory response to some types of cancer, stimulate the immune response against unwanted intestinal microorganisms including viruses, and help control serum cholesterol levels. As with the other organisms listed on this page, more research must be performed to validate these claims.
Lactobacillus delbrueckii subspecies bulgaricus is most familiar as one of two organisms used in the manufacture of yogurt. In the United States viable Lactobacillus bulgaricus culture must be added to yogurt to meet the standard of identity requirements. Some studies suggest that strains of Lactobacillus bulgaricus improve the metabolism of lactose and stimulate the immune response in the intestinal tract.
The formal name of Lactobacillus rhamnosus is Lactobacillus casei subspecies rhamnosus. It differs from Lactobacillus acidophilus in that it is generally less tolerant to digestive enzymes and is more transient in the human intestines. Lactobacillus rhamnosus has been used to deliver and release lactase enzyme throughout the stomach and small intestine to hydrolyze (break down) lactose. Certain strains of this organism have been shown to stimulate an immune response against foreign intestinal organisms, and prevent rotoviral or Clostridium difficile-induced diarrhea.
Streptococcus thermophilus, along with Lactobacillus bulgaricus, must be added to the yogurt blend to meet the requirements to be called yogurt in the United States. Some research indicates that the high level of lactase enzyme activity of this organism makes it an even better candidate for improving lactose digestion in the intestinal tract than Lactobacillus acidophilus and other lactobacilli species. Other research suggests that Streptococcus thermophilus can improve the nutritional value of foods by making micronutrients available to the host.
Lactobacillus casei subspecies casei is a probiotic bacterium that has been used for centuries in traditional cultured milks in Asia, such as the Yakult beverage from Japan. It is a highly prolific organism and has good resistance to digestive enzymes. Some studies have shown strains of Lactobacillus casei have the ability to stimulate the immune response in the intestinal tract.
Bifidobacterium bifidum resides in the colon where it can be found at high concentrations. It composes a majority of the beneficial microflora that produce acids to retard colonization of putrefactive bacteria such as E. coli, Clostridium, and Salmonella. Strains of this species have been used in therapeutic preparations for the treatment of the following: digestive disorders in infants, enterocolitis, constipation, cirrhosis of the liver, imbalance of intestinal flora following antibiotic therapy, and have also been used for promotion of intestinal peristalsis (moving food through the digestive tract).