Changes in the Composition and Function of the Human Salivary Microbiome After Heart Transplantation: A Pilot Study

Introduction: Interactions between our commensal microbes and immune system are well recognized but the impact of immunosuppression on this relationship is less well characterized, particularly outside of the gastrointestinal tract. In this pilot case-control study, we examined microbial composition and inferred function in the saliva of patients after heart transplantation. Methods: Saliva samples were collected from 26 healthy adolescent and adult heart transplant patients and 27 healthy non-transplant controls. Bacterial DNA was isolated and the V3 and V4 regions of the 16S rRNA gene were sequenced. Measures of bacterial diversity and inferred function were calculated using the software packages DADA2, Phyloseq, QIIME, PICRUSt and STAMP. Results: Transplant patients were on average 51.6 +/- 18.2 years of age and 8.6 +/- 5.3 years post-transplant. Both alpha (p = 0.0009) and beta (p = 0.001) diversity differed significantly between the groups, and there were statistically significant changes (p < 0.01) in 101 individual functional pathways. Discussion: We conclude that the effects of chronic immunosuppression on bacterial composition and function in the oropharynx appear relatively subtle with no obvious ill effects on patient health. Full interpretation is limited by our lack of knowledge for many of the bacterial functional pathways.