Regarding the cultures of lactobacilli that are consumed in capsules, there are different requirements the culture should meet in order to be truly effective:
1. Firstly they should endure over time (many probiotics on the market have a short life span).
2. Once ingested, the bacterium must be able to withstand both passage through the gastric juices (acids) and the bile salts (alkaline).
3. If it reaches the intestine undamaged, it should adhere to the intestinal walls and compete effectively with the pathogenic bacteria already present.
4. Finally it has to be able to carry out a series of nutritional (production of the enzymes necessary for digestion of dairy products, production of vitamin B etc.) and antimicrobial activities.