Abstract
Alterations to the intestinal microbiome prior to bone marrow transplant (BMT) are associated with post-BMT mortality, and distinct compositional changes (increase in Firmicutes and decrease in Bacteroidetes) are present in adults with cardiovascular (CV) disease. We hypothesize that alterations to the intestinal microbiome occur in children after pediatric heart transplant (HTx). Pre-HTx and sequential post-HTx stool specimens (2 week, 1 month) were collected in children undergoing HTx between 9/2018 - 3/2019. Bacterial DNA was extracted, and the resulting nucleic acid was processed through an Illumina MiSeq 16S sequencing pipeline. Separate regions of the highly variable areas of the 16S rRNA gene, V1V3 and V4, were targeted for sequencing. Resulting raw sequences were analyzed utilizing the UPARSE algorithm for clustering of sequences into operational taxonomic units (OTUs) and the SILVA v123 database for taxonomic classification of each OTU. Pre-HTx and sequential post-HTx specimens were compared using ANOVA with Benjamini-Hochberg Correction. Pre-HTx and 2 post-HTx (median 14 days post-HTx, 31 days post-HTx) stool specimens were collected in 13 patients (median age 6.7 years, IQR 3.5-9.9) during the study period. There are notable differences in the intestinal bacterial composition between pre-HTx and post-HTx specimens at the Phyla (Fig 1A) and Genus (Fig 1B) levels. There is a decrease in Bacteroidetes (Bacteroides) and increase in Firmicutes and Escherichia/Shigella post-HTx. Enterococcus was absent in pre-HTx specimens but abundant in post-HTx specimens (Fig 1C). Alterations to the intestinal microbiome are immediately present after HTx. These include previously described deleterious changes found in adults with CV disease (increase in Firmicutes & decrease in Bacteroidetes) and in critically ill adults (increase in Enterococcus). The impact of the intestinal microbiome on pediatric HTx outcomes warrants investigation and may identify novel modifiable risk factors.
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