WASHINGTON (FRONTLINE MEDICAL NEWS) – During and after liver transplant, the reaction of the intestinal microbiota may be a critical determinant of outcomes; preliminary data from a cohort study may provide some clarification of what modulates gut microbiota post transplantation and shed light on predictive factors.

Anna-Catrin Uhlemann , MD, PhD, of Columbia University Medical Center, New York, noted that several studies in recent years sought to clarify influences on gut microbiota in people receiving liver transplants, but “there are still a number of important gaps in knowledge, including what exactly is the longitudinal evolution of the host transplant microbiome and what is the predictive value of pre- and early posttransplant dysbiosis on outcomes and complications.”

She and her coinvestigators hypothesized that colonization of multidrug resistant (MDR) organisms are major drivers of post–liver transplant dysbiosis, and launched a prospective longitudinal cohort study 3 years ago. So far, 125 patients have been enrolled either before their transplant or 1 week after, and completed 1-year follow-up. Fecal samples were collected before transplant, weekly during hospitalization, and at 3-month intervals for a year.

The researchers collected more than 1,000 samples to screen for colonization by the following MDR organisms: carbapenem-resistant Enterobacteriaceae (CRE), Enterobacteriaceae resistant to third-generation cephalosporins (ESBL), and vancomycin-resistant enterococci (VRE). Over the 1-year follow-up period, 19% (P =.031) of patients had CRE colonization associated with subsequent infection, 41% (P = .003) had ESBL colonization, and 46% (P = .021) had VRE colonization, Dr. Uhlemann said at the annual meeting of the American Association for the Study of Liver Diseases. The researchers then selected 484 samples for sequencing of the 16S ribosomal RNA gene to determine the composition of gut microbiota.

The study used two indexes to determine the alpha diversity of microbiota: the Chao index to estimate richness and the Shannon diversity index to determine the abundance of species in different settings. “We observed dynamic temporal evolution of alpha diversity and taxa abundance over the 1-year follow-up period,” Dr. Uhlemann said. “The diagnosis, the Child-Pugh class, and changes in perioperative antibiotics were important predictors of posttransplant alpha diversity.”

The study also found that Enterobacteriaceae and enterococci increased post transplant in general and as MDR organisms, and that a patient’s MDR status was an important modulator of the posttransplant microbiome, as was the lack of protective operational taxonomic units (OTUs).

The researchers evaluated the relative abundance of taxa and beta diversity. For example, pretransplant patients with a Model for End-stage Liver Disease (MELD) score greater than 25 showed enrichment of Enterobacteriaceae as well as different taxa of the Bacteroidiaceae, while those with MELD scores below 25 showed enrichment of Veillonellaceae. “The significance of this is not clear yet,” Dr. Uhlemann said.

Liver disease severity can also influence gut microbes. Those with Child-Pugh class C disease have the highest numbers in terms of richness and lowest in terms of diversity, Dr. Uhlemann said. “However, at the moment when we are looking at the differential abundance of the taxa, we don’t see quite as clear a pattern, although we noticed in the high group a higher abundance of Bacteroidiaceae,” she said.

Hepatitis B and C patients also presented divergent microbiota profiles. Hepatitis B virus patients “in general are always relatively healthy, and we actually see that these indices are relatively preserved,” Dr. Uhlemann said. “When we look at hepatitis C, however, we see that these patients are starting off quite low and then have an increase in alpha-diversity measures at around month 6.” A subset of patients with alcoholic liver disease also didn’t reach higher Chao and Shannon levels until 6 months after transplant.

“We also find that adjustment of periodic antibiotics for allergy or history of prior infection is significantly associated with a decrease in alpha diversity several months into the posttransplant course,” said Dr. Uhlemann. This is driven by an increase in the abundance of Enterococcaceae and Enterobacteriaceae. “And when we look at MDR colonization as a predictor of alpha diversity, we see that those who have MDR colonization, irrespective of the species, also have the lower alpha diversity.”

The researchers also started to look at pretransplant alpha diversity as a predictor of transplant outcomes, and while the analysis is still in progress, the Shannon indices were significantly different between patients who died and those who survived a year. “There was a trend for significant differences for posttransplant infection and the length of the hospital stay,” Dr. Uhlemann said. “However, we did not see any association with posttransplant ICU readmission, rejection, or VRE complications.”

She added that future analyses are needed to further evaluate the interaction between the clinical comorbidities in the microbiome and vice versa.

Dr. Uhlemann disclosed links to Merck.


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