Chung The, H. | Search bioRxiv

bioRxiv2022

Mucosal microbiomes and Fusobacterium genomics in Vietnamese colorectal cancer patients

Perturbations in the gut microbiome have been linked to the promotion and prognosis of colorectal cancer (CRC), with the colonic overabundance of Fusobacterium nucleatum shown as the most consistent marker. Despite the increasing health burden inflicted by CRC in low- and middle-income countries like Vietnam, the CRC-specific microbiome in these populations remains underexplored. Here we conducted a study in Vietnam to enrol 43 CRC patients (cases) and 25 patients with non-cancerous colorectal polyps (controls) between December 2018 and January 2020. Our study investigated the mucosal microbiome signature and genomic diversity of Fusobacterium in Vietnamese CRC patients, using a combination of 16S rRNA gene profiling, anaerobic microbiology, and whole genome sequencing. We found that several oral bacteria, including F. nucleatum and Leptotrichia, were significantly more abundant in the tumour mucosa, and these two bacteria were also more enriched in tumours of advanced CRC stages (III-IV). We obtained 53 Fusobacterium genomes from the saliva, tumour and non-tumour mucosa of six CRC patients. Isolates from the gut mucosa belonged to diverse F. nucleatum subspecies (nucleatum, animalis, vincentii, polymorphum) and a potential new subspecies of F. periodonticum. The Fusobacterium population within each individual was distinct and in many cases diverse, with minimal intra-clonal variation. Phylogenetic analyses showed that within each individual, tumour-associated Fusobacterium were clonal to those isolated from non-tumour mucosa, but distantly related to those isolated from saliva. Genes encoding major virulence factors (Fap2 and RadD) showed variability in length and evidence of horizontal gene transfer. Our work provides a framework to understand the genomic diversity of Fusobacterium within the CRC patients, which can be exploited for the development of CRC diagnostic and therapeutic options targeting this oncobacterium.

microbiology↗

bioRxiv2021

Exploring the genomic diversity and antimicrobial susceptibility of Bifidobacterium pseudocatenulatum in the Vietnamese population to aid probiotic design

Bifidobacterium pseudocatenulatum is a member of the human gut microbiota, and has previously been used as a probiotic to improve gut integrity and reduce inflammatory responses. We showed previously that B. pseudocatenulatum was significantly depleted during dysenteric diarrhea, suggesting the organism may aid in recovery from diarrhea. Here, in order to investigate its probiotic potential, we aimed to assess the genomic diversity and predicted metabolic profiles of B. pseudocatenulatum found colonizing the gut of healthy Vietnamese adults and children. We found that the population of B. pseudocatenulatum from each individual was distinct and highly diverse, with intra-clonal variation attributed to gain or loss of carbohydrate utilizing enzymes. The B. pseudocatenulatum genomes were enriched with glycosyl hydrolases that target plant-based non-digestible carbohydrates (GH13, GH43), but not host-derived glycans. Notably, the exopolysaccharide biosynthesis region from organisms isolated from healthy children showed greater genetic diversity, and was subject to a high degree of genetic modification. Antimicrobial susceptibility testing revealed that the Vietnamese B. pseudocatenulatum were uniformly susceptible to beta-lactams, but exhibited variable resistance to azithromycin, tetracycline, ciprofloxacin and metronidazole. The genomic presence of ermX and tet variants conferred resistance against azithromycin and tetracycline, respectively; ciprofloxacin resistance was associated with mutation(s) in the quinolone resistance determining region (GyrA, S115 and/or D119). Our work provides the first detailed genomic and antimicrobial resistance characterization of B. pseudocatenulatum found in the Vietnamese population, which could inform the next phase of rational probiotic design. ImportanceBifidobacterium pseudocatenulatum is a probiotic candidate with potential applications in several health conditions, but its efficacy is largely strain-dependent and associated with distinct genomic and biochemical features. However, most commercial probiotics have been developed by Western institutions, which may not have ideal efficacy when administered in developing countries. This study taps into the underexplored diversity of the organism in Vietnam, and provides more understanding to its lifestyles and antimicrobial susceptibility. These data are key for selecting an optimal probiotic candidate, from our established collection, for downstream investigations and validation. Thus, our work represents a model in identifying and characterizing bespoke probiotics from an indigenous population in a developing setting.

microbiology↗