Shared mechanisms among probiotic taxa: implications for general probiotic claims

Shared probiotic mechanisms and their taxonomic distribution. ▪ •Shared mechanisms within taxonomic groups go beyond strain-specific effects.•Probiotic benefits may derive from mechanisms that are shared among strains.•A shared mechanism may lead to a shared benefit exerted by most members of a taxon.•One example of a shared mechanism is short chain fatty acid production.•Another shared mechanism is cell surface components that enhance GI survival.•Another shared mechanism is effector molecules which signal the immune system.•Not all microbes expressing these mechanisms are necessarily probiotics or beneficial.•Shared mechanisms may allow assignment of probiotic benefits to taxa beyond a strain. Strain-specificity of probiotic effects has been a cornerstone principle of probiotic science for decades. Certainly, some important mechanisms are present in only a few probiotic strains. But scientific advances now reveal commonalities among members of certain taxonomic groups of probiotic microbes. Some clinical benefits likely derive from these shared mechanisms, suggesting that sub-species-specific, species-specific or genus-specific probiotic effects exist. Human trials are necessary to confirm specific health benefits. However, a strain that has not been tested in human efficacy trials may meet the minimum definition of the term ‘probiotic’ if it is a member of a well-studied probiotic species expressing underlying core mechanisms and it is delivered at an effective dose.