ABSTRACT The beneficial effects attributed to Bifidobacterium are thought to arise from their host immunomodulatory capabilities, which are likely to be species- and even strain-specific. However, their strain-specificity in direct and indirect immune modulation remain largely uncharacterized. We have shown that B. pseudolongum UMB-MBP-01, a murine isolate, is capable of suppressing inflammation and reducing fibrosis in vivo . To ascertain the mechanism driving this activity and to determine if it is specific to UMB-MBP-01, we compared it to B. pseudolongum type strain ATCC25526 of porcine origin using a combination of in vitro and in vivo experimentation and comparative genomics approaches. Despite many shared features, we demonstrate that these two strains possess distinct genetic repertoires in carbohydrate assimilation, differential activation signatures and cytokine responses in innate immune cells, and differential effects on lymph node morphology with unique local and systemic leukocyte distribution. Importantly, the administration of each B. pseudolongum strain resulted in major divergence in the structure, composition, and function of gut microbiota. This was accompanied by markedly different changes in intestinal transcriptional activities, suggesting strain-specific modulation of the endogenous gut microbiota as a key to host responses of immune modulation and changes in intestinal B. pseudolongum strains. These observations highlight the importance of strain-specificity characteristics of Bifidobacterium for prophylactic supplementation for immune modulation and advance our understanding of the mechanisms which drive the association between Bifidobacterium and health benefit.

Strain-specific alterations in gut microbiome and host immune responses elicited by Bifidobacterium pseudolongum