Synergistic vs. complementary synbiotics: the complexity of discriminating synbiotic concepts using a Lactiplantibacillus plantarum exemplary study.

Synbiotics are defined as "a mixture comprising live microorganisms and substrate(s) selectively utilized by host microorganisms that confers a health benefit on the host". The definition discriminates between synergistic and complementary synbiotics. Synergistic synbiotics involve a direct interaction between the substrate and co-administered microbe(s), while complementary synbiotics act through independent mechanisms. Here, we evaluate the complexity of discrimination between these two synbiotic concepts using an exemplary study performed with a panel of Lactiplantibacillus plantarum (L. plantarum) strains to identify strain-specific synergistic synbiotics that eventually turned out to work via a complementary synbiotic mechanism. This study highlights that assessing the in situ selectivity of synergistic synbiotics in the intestinal tract is challenging due to the confounding effects of the substrate ingredient on the endogenous microbiome, thereby raising doubts about the added value of distinguishing between synergistic and complementary concepts in synbiotics.