Andrea Dame

OBJECTIVE: This study aims to validate the existence of a microbiome within intraductal papillary mucinous neoplasm (IPMN) that can be differentiated from the taxonomically diverse DNA background of next-generation sequencing procedures. DESIGN: We generated 16S rRNA amplicon sequencing data to analyse 338 cyst fluid samples from 190 patients and 19 negative controls, the latter collected directly from sterile syringes in the operating room. A subset of samples (n=20) and blanks (n=5) were spiked with known concentrations of bacterial cells alien to the human microbiome to infer absolute abundances of microbial traces. All cyst fluid samples were obtained intraoperatively and included IPMNs with various degrees of dysplasia as well as other cystic neoplasms. Follow-up culturing experiments were conducted to assess bacterial growth for microbiologically significant signals. RESULTS: Microbiome signatures of cyst fluid samples were inseparable from those of negative controls, with no difference in taxonomic diversity, and microbial community composition. In a patient subgroup that had recently undergone invasive procedures, a bacterial signal was evident. This outlier signal was not characterised by higher taxonomic diversity but by an increased dominance index of a gut-associated microbe, leading to lower taxonomic evenness compared with the background signal. CONCLUSION: The 'microbiome' of IPMNs and other pancreatic cystic neoplasms does not deviate from the background signature of negative controls, supporting the concept of a sterile environment. Outlier signals may appear in a small fraction of patients following recent invasive endoscopic procedures. No associations between microbial patterns and clinical or cyst parameters were apparent.

The gut microbiota plays a pivotal role in maintaining human health with dysbiosis linked to a variety of diseases. Metagenome sequencing and robust statistical analysis have linked specific strains, including the gut bacterium Campylobacter concisus , to Crohn’s disease and ulcerative colitis, together known as inflammatory bowel disease (IBD). However, the roles of this and other strains in disease progression remain to be investigated. Herein, we assess the contribution of C. concisus secondary metabolites to inflammation. Through untargeted metabolomics, we identified a diverse array of nineteen indole-containing metabolites produced by C. concisus , including trisindoline, previously isolated from a marine bacterium. Collectively, these metabolites modulate inflammatory responses by significantly inducing the release of proinflammatory cytokines interleukin (IL)-1β, IL-6, IL-8, and MCP-1. The metabolites act through the aromatic hydrocarbon receptor arylhydrocarbon receptor and in vivo intravital imaging revealed a marked increase in the recruitment and activation of immune cells, specifically neutrophils and macrophages, following the administration of trisindoline. Several indole metabolites also exhibited antimicrobial activity against commensal strains that facilitate a proper immune response. Our study provides a possible rationale for the association of C. concisus with IBD and underscores the complex interplay between gut bacteria and host immunity. The identification of indole-derived secondary metabolites as key modulators of inflammation offers new avenues for therapeutic intervention.