Metronidazole pretreatment remodeled gut microbiota composition and significantly delayed islet allograft rejection in a murine model, with Mendelian randomization analyses identifying several anaerobe-associated gut microbial taxa potentially relevant to transplant rejection risk.
Key Findings
Results
Metronidazole pretreatment significantly delayed islet allograft rejection in a murine islet transplantation model.
A murine islet transplantation model was used to assess the effects of metronidazole pretreatment on allograft survival and function.
Metronidazole treatment remodeled gut microbiota composition alongside delayed rejection.
The study used 16S rRNA sequencing to characterize treatment-associated changes in gut microbial composition.
The findings are described as 'hypothesis-generating' and warranting further mechanistic investigation.
Results
Metronidazole treatment reduced CD4+ T-cell infiltration around the allograft and Th17-related inflammatory responses.
Immunohistochemistry and flow cytometry were used to evaluate post-transplant immune responses after metronidazole pretreatment.
Reduction in CD4+ T-cell infiltration was observed in the area surrounding the allograft.
Th17-related inflammatory responses were reduced following metronidazole treatment.
These immune changes occurred in the context of gut microbial remodeling by metronidazole.
Results
Mendelian randomization analyses identified several anaerobe-associated gut microbial taxa potentially relevant to transplant rejection risk.
An exploratory two-sample Mendelian randomization (MR) analysis was performed using human GWAS data.
The composite outcome assessed was transplant failure or rejection.
Identified taxa included the family Defluviitaleaceae and the genera Intestinibacter, Bilophila, Ruminococcus, and Eubacterium fissicatena.
All identified taxa are anaerobe-associated gut microbial groups.
The analysis is described as 'exploratory' and used to 'prioritize' rather than confirm associations.
Results
Integrative biological annotation of MR-identified taxa highlighted glycosylation-related pathways and prioritized ST3GAL4 for subsequent expression assessment.
Biological annotation was used to prioritize candidate host pathways downstream of the MR-identified microbial taxa.
Glycosylation-related pathways were highlighted as potentially relevant.
ST3GAL4, a gene involved in glycosylation, was prioritized for expression assessment in the murine transplant model.
This approach linked human GWAS-based MR findings to functional pathway candidates for experimental follow-up.
Results
Metronidazole pretreatment remodeled gut microbiota composition in the murine model.
16S rRNA sequencing was performed to characterize treatment-associated changes in gut microbial composition.
Metronidazole, an antibiotic with activity against anaerobes, was used as the pretreatment agent.
Changes in gut microbial communities were documented alongside altered allograft rejection outcomes.
The remodeling specifically targeted anaerobe-associated microbial communities, consistent with metronidazole's known spectrum of activity.
What This Means
This research suggests that the community of bacteria living in the gut — particularly anaerobic (oxygen-avoiding) bacteria — may play a role in how the immune system responds to transplanted organs or tissues. In a mouse model of islet (insulin-producing cell) transplantation, the researchers found that treating mice with metronidazole, an antibiotic commonly used to target anaerobic bacteria, changed the composition of gut bacteria and noticeably delayed the immune system's rejection of the transplanted tissue. The treated mice also showed lower levels of immune cells (CD4+ T-cells and Th17 cells) attacking the transplant, suggesting a dampened rejection response linked to changes in gut microbes.
To explore whether these findings might be relevant to humans, the researchers also conducted a statistical analysis using genetic data from large human studies. This type of analysis, called Mendelian randomization, uses genetic variants as tools to look for potential causal relationships without running a clinical trial. They identified several specific anaerobic bacterial groups — including Defluviitaleaceae, Intestinibacter, Bilophila, Ruminococcus, and Eubacterium fissicatena — as potentially associated with transplant failure or rejection risk in humans. Further analysis pointed to a biological process called glycosylation, and specifically a gene called ST3GAL4, as a possible link between gut bacteria and transplant outcomes.
This research suggests there may be a connection between the gut microbiome and transplant rejection that could one day be targeted therapeutically, though the authors emphasize these findings are hypothesis-generating and require further mechanistic investigation before any clinical conclusions can be drawn. The combination of animal experiments and human genetic data represents an early-stage but multi-layered approach to understanding how gut bacteria might influence immune responses after transplantation.
Liu Y, Tian Y, Pu C, Yang Y, Peng X, Zhu H, et al.. (2026). Metronidazole-mediated gut anaerobe remodeling is associated with transplant rejection.. Frontiers in cellular and infection microbiology. https://doi.org/10.3389/fcimb.2026.1874387