It is beneficial bacteria. However, contrary to normal thinking, not all bacteria cause harm or are bad for us. Some of them are good and one of them is acidophilus. Many factors decrease the number of good bacteria that live and work in the gastrointestinal tract and protect us from harmful disease-causing bacteria, aging, alcohol, antibiotics, diet deficiencies, drugs, medications, narcotics, nicotine, and stressful living. Food is digested in the alimentary canal, mouth and stomach, and finally in the intestines.
In the intestines, partially-digested food is metabolized by millions and millions of microorganisms (good bacteria), working simultaneously and synergistically. If there is too small a colony of good bacteria, such as acidophilus digestion can be impaired, we can not get full nutritional value from foods,fewer key vitamins will be synthesized and the immune system may be rendered less effective .Acidophilus can be found in some quality yogurts and other traditional foods naturally. It is often added to milk or sold as a capsule, which contains one or more of the following bacteria which aid in digestion: -Lactobacillus acidophilus, Lactobacillus casei, Lactobacillus bulgaricus Bifidobacterium bifidum and Streptococcus thermophilus .Only L. acidophilus is the true acidophilus strain, but many producers (mainly in the US) use it as a more generic name for mixtures of bacteria, one of which is L. acidophilus.