| dc.description.abstract | Background: Early detection of colorectal cancer (CRC) in screening programs is important to reduce development of CRC from precursor lesions. The CRCbiome study, nested within the screening pilot Bowel Cancer Screening in Norway (BCSN), aims to identify microbial biomarkers for early CRC detection. Preliminary results from the CRCbiome study have shown diet, lifestyle and sociodemographic differences and differences in CRC incidence between the populations of the two screening centers (Bærum and Moss). The main purpose of the master’s project was to investigate regional gut microbiome differences and investigate whether there was an association between diet, lifestyle and sociodemographic factors and the microbiome profiles.
Methods: A total of 1036 participants from the CRCbiome study were included. Regional microbial differences were examined using three regional determinants: 1) screening center (Bærum and Moss), 2) the centrality class of their address (centrality class 1, 2 and >3), and 3) driving time from their home to the screening center (short and long driving time). Comparative metagenomic analysis of gut microbiome was performed by investigating the diversity within-groups (α-diversity) and between-groups (β-diversity), followed by differential abundance analysis of bacterial species. Connections between differentially abundant bacteria and diet, lifestyle and sociodemographic factors were investigated using Spearman correlation coefficients as inputs in principal component analysis (PCA) and hierarchical clustering.
Results: Overall, there were no regional differences in α-diversity for any of the three regional determinants investigated, but small differences in β-diversity were observed, with deviating findings when analyzing the age segment of 55-65 years, males, those with no neoplasia and those with advanced neoplasia. β-diversity did not significantly differ when comparing centrality class 2 versus class >3. Analysis of differential abundance revealed enrichment in beneficial species associated with healthier diet and lifestyle, and higher socioeconomic status, for participants affiliated to the Bærum screening center, for participants residing centrally and for those having short driving time to the screening center. The differences were mainly driven by the Firmicutes phylum, most prominently in the Bacilli and Clostridia classes.
Conclusion: De-central residency and long driving time were associated with CRC risk factors and correlated with disadvantageous microbiome profiles. The study also found that beneficial microbiome profiles were correlated with factors known to reduce the risk of developing CRC. However, while the results provide valuable insights into the regional differences in the gut microbiome, further research is required to fully comprehend the impact of the differences. | |