A critical evaluation of the factors affecting the survival and persistence of beneficial bacteria in healthy adults.

The efficacy of a probiotic depends on its ability to survive and persist in the digestive tract. Regulatory agencies around the world recommend minimum dosages in order for a product to be termed a probiotic. However, the effect of dosage on the survival of the bacteria in the gut - the primary objective of probiotic administration - has not been critically evaluated. We performed a systematic literature review to assess the available data on the survival rate, during gastrointestinal transit, of probiotic bacteria that were orally administered to healthy adults. We also evaluated the persistence of the administered strain(s) after discontinuation of treatment and the potential role played by the food matrix in which probiotics have been administered. From a regulatory perspective, the profile of the target population is key to establishing the efficacy of probiotics. Therefore, we focussed on subjects without disease conditions. We evaluated 17 studies of single strains and 13 studies of multi-strain products, which reported survival and persistence outcomes. Persistence in the gut and recovery from stool were strain dependent. When the administered dose was higher than 1010 cfu/day, the probiotic could be recovered from stool regardless of the strain used. Treatment duration did not affect faecal recovery. Thus, dosage recommendations for probiotics by regulatory agencies are lower than that required for a strain to survive, persist and be efficacious in the gut.