Bile microbiota: new insights into biliary complications in liver transplant recipients

Biliary complications represent a major problem associated with liver transplantation. This report represents the first study to use high-throughput 16S ribosomal RNA (rRNA) gene sequencing to assess bile microbiota within bile samples of liver transplant recipients with biliary complications. Our goal in this report was to identify the species and abundance of microbes and examine the potential for microbial involvement of bile in liver transplantation patients with biliary complications.

Liver transplant recipients treated at our center over the period from September 2015 to June 2017 were enrolled in the study. Patients satisfying the inclusion criteria were divided into two groups, control (N=13) and symptom (N=10). Sequencing of 16s rDNA was then performed on bile samples from both groups.

The main bacterial phyla of bile samples in the symptom group included Proteobacteria (55.19%), Firmicutes (32.36%), Actinobacteria (10.24%) and Bacteroidetes (1.23%) and the main bacterial genera were Pseudomonas (23.31%), Klebsiella (18.42%), Lactococcus (9.61%), Rhodococcus (9.59%) and Rhizobium (5.08%). Proteobacteria and Staphylococcus were enriched in the symptom group (P<0.05), whereas Firmicutes (P<0.05) and Enterococcus (P<0.01) were enriched in the control group. Pathways involved as determined with use of the Kyoto Encyclopedia of Genes and Genomes (KEGG), revealed that metabolism pathways of glyoxylate and dicarboxylate, porphyrin and chlorophyll, arginine and proline, glycine, serine and threonine, as well as the bacterial secretion system were all enriched in bile samples from the symptom group (P<0.05).

Clear differences exist in microbial species distribution in bile samples from the symptom versus control group. The species and pathways enriched in bile samples within the symptom group may be involved in the pathogenesis of biliary complication after liver transplantation.