A survey on established and novel strains for probiotics applications

Probiotics are a heterogeneous group of nonpathogenic bacteria that are functionally defined by their ability to produce a health benefit to the host when provided in adequate amounts. In recent years, a number of rigorous researches based on double blind randomized placebo-controlled human intervention trials have been carried out, better supporting the idea that our health can be positively affected by the regular administration of specific probiotics. Indeed, the use of probiotics has recently moved from concept to actual demonstration of specific benefits by specific microorganisms for specific populations. For this reason, the effects of several microbial strains that are marketed as established probiotics have been increasingly tested in well-conducted clinical studies for the treatment and prevention of selected disease states, both inside and outside the gastrointestinal tract. In the meantime, there is an interest in selecting novel candidate probiotic strains for particular subject groups. In this survey, we focused on both aspects, therefore literature data were collected and analysed (297 papers) on the strains applied for clinical trials in the last five years (2008-2013). Information on the identity of the strain, strain identification number and the kind of application were extracted and presented, to show that only a limited number of species includes the majority of probiotic strains. Also, systematic reviews within the Cochrane Library were analyzed and diseases treated were grouped according to the categories proposed on ClinicalTrials.gov website (http://www.clinicaltrials.gov/), i.e. macro areas following the human organ or system involved. Besides the standard use of alive bacterial cells to be ingested, literature data on health benefits deriving from inactivated bacterial cells have been reported and are summarized. Also, not all the strains proved to be effective for some diseases, confirming that beneficial properties are strain- and application-dependent. Finally, the perspectives in the field of probiotics brought about genomics are briefly reviewed