Evidence of Probiotic Strain Specificity Makes Extrapolation of Results Impossible From a Strain to Another, Even From the Same Species

Introduction: objectives

According to the definition, probiotics are: “Live microorganisms which when administered in adequate amounts confer a health benefit on the host.” Only a limited number of microbial strains have been properly studied and have shown beneficial properties for humans. The European Food Safety Authority (EFSA) highlighted as critical factors for probiotic health claim submissions genetic typing of the strain(s), internationally recognized naming protocols and evidence of consistency in the final product. In this paper, I will summarize what is known on similarities and differences between probiotic microorganisms and properties. I will provide examples of strain specific properties, which demonstrate that extrapolation of results from a strain to another should be banned.

Abstract

Clinical trials show that some probiotic effects are observed with specific strains but not in control strains. The strains compared were often members of different species or even genus. There is a tendency to believe that some extrapolation of results could be possible for microorganisms of the same species, and this is especially done by some companies selling products that were not studied and using studies performed with different strains. However, several studies compared the composition, characteristics, and physiological properties of probiotic strains in comparison to very closely related strains within the same species. These studies show strain or family-specific differences. This paper will provide examples showing that related bacterial strains can differ significantly in their genotype, phenotype, and properties. The implications of this strain-specificity are that (1) for commercial products, documentation of health effects must be conducted on the specific strain contained in the product; (2) one should avoid any extrapolation of positive or negative effects between probiotic strains; (3) meta-analysis of the effect of probiotics with different active molecules should be avoided; (4) one should not call a probiotic a strain that has not been studied just on the basis that it is taxonomically related to a well-proven probiotic strain. These rules are presently frequently violated.

Keywords

probiotics, strain specificity, Lactobacillus, Bifidobacterium