Altered Gut Microbial Fermentation and Colonization with Methanobrevibacter smithii in Renal Transplant Recipients.

Renal transplant recipients (RTRs) often suffer from posttransplant diarrhea. The observed dysbiosis in RTR may influence the fermentation processes in the gut. In this study, we aimed to investigate whether fermentation differs between RTRs and healthy controls (HCs), by measuring breath H ₂ and CH ₄ concentrations. Additionally, we determined the fecal presence of the methanogen Methanobrevibacter smithii ( M. smithii ), which plays a main role in the process of methanogenesis. Data from the TransplantLines Biobank and Cohort Study (NCT03272841) was used. A total of 142 RTRs and 77 HCs were included. Breath H ₂ concentrations in RTRs were not significantly different from HCs. Breath CH ₄ concentrations in RTRs were significantly lower compared with HCs (median [interquartile range (IQR)] 7.5 [3.9-10.6] ppm vs. 16.0 [8.0-45.5] ppm, p < 0.001). M. smithii was less frequently present in the feces of RTRs compared to HCs (28.6% vs. 86.4% resp., p < 0.001). Our findings regarding the altered methanogenesis in the gut of RTRs show similarities with previous results in inflammatory bowel disease patients. These findings provide novel insight into the alterations of fermentation after renal transplantation, which may contribute to understanding the occurrence of posttransplant diarrhea.