: To Survive, or Not to Survive the Gastrointestinal Tract, That Is the Question!

The probiotic market is increasing world-wide as well as the number of products marketed as probiotics. Among the latter, many products contain strains at several dosages. However, the scientific evidence that should support the probiotic status of those strains is often contradictory. This review analyses the scientific literature aimed to assess the ability of strains to survive the human gastrointestinal tract by discussing the scientific validity of the methods applied for the bacterial recovery and identification from stool samples. This review highlights that in most of the intervention studies reviewed, the identification of strains from stools was not carried out with the necessary taxonomic accuracy to avoid their misidentification with , a common human commensal and a species phylogenetically close to . Moreover, this review highlights how critical the accurate taxonomic identification of in metagenomics-based studies can be.