Investigating the oral microbiome in hematopoietic cell transplants - ABSTRACT While hematopoietic cell transplant (HCT) is an effective curative treatment for children with various malignant and non-malignant diseases, it is also associated with several complications, such as oral mucositis (OM) and bloodstream infections (BSI). The loss of mucosal integrity in OM not only results in ulcerative lesions that are a significant source of pain, but also, the compromised mucosal barrier becomes susceptible to bacterial translocation and predisposes patients to BSI. Several studies have reported disruptions of the oral microbiome in patients undergoing HCT, and this was linked to OM. In addition, bacterial species present in the oral cavity (i.e., viridans group streptococci) have been implicated in BSI. While this establishes the role of oral microbial species in OM and BSI pathogenesis, nearly all of this research is limited to adults, despite the high prevalence of OM (70-80%) and BSI (15-65%) in children. Furthermore, the current standard for diagnosing BSI is culture- based method that is not comprehensive or high enough resolution to distinguish all species, including the oral streptococci. It is crucial to accurately define the blood microbial signature of this high-risk cohort to determine if the oral cavity is a reservoir of organisms causing BSI, and if so, to guide preventive approaches. For Aim 1 we will conduct a longitudinal study in children undergoing HCT at Nationwide Children’s Hospital to understand the impact of oral microbial species during the development and progression of OM and BSI. Our pilot study revealed overall microbial community composition changed as children underwent HCT. We will now expand our sample size to define the oral microbial community changes at the species level and determine the relationship of these changes to oral mucositis and bloodstream infections. Site-specific oral samples (plaque, tongue, mucosa) will be collected at a minimum of four time points. Both species level bacterial and fungal composition by 16S/ITS2 amplicon sequencing, and absolute abundance by qPCR will be analyzed. OM incidence and severity will be scored, and all BSI occurrences will be recorded. The relationship of microbial community composition with time course, oral hygiene, OM score, and BSI occurrence will be examined. Our preliminary 16S amplicon data revealed polymicrobial profiles containing microbial species common to the oral cavity in the bloodstream of subjects with BSI. For Aim 2 we will comprehensively define the bloodstream microbial profile in children receiving HCT by longitudinally collecting blood samples from all subjects and comparing their bloodstream microbial profile in the presence and absence of BSI. To determine if the oral cavity is the likely source of bloodstream infection-associated microbes, we will use high-resolution bioinformatic tools (DADA2) on our amplicon data and analyze the concordance of species detected in blood samples with those detected in the oral cavity. The most likely oral source (plaque, tongue or mucosa) will also be examined. The results of these studies will inform future preventive and therapeutic strategies to reduce OM and BSI burden. They will also lay a foundation for future investigations of therapies and mechanistic studies of bloodstream invasive oral microbes.
