Comparison of bacterial community profiles from large intestine specimens, rectal swabs, and stool samples.

The human gastrointestinal tract contains a complex and dynamic population of microorganisms, known as the gut microbiota. Although interest in the role of the gut microbiota in human health has increased in recent years, there remains no standard sampling protocol for analyzing these organisms. Here, we aimed to characterize the microbial composition of distinct segments of the large intestine and to determine whether rectal swabs are suitable for identifying colon microbiota. A total of 100 participants who underwent screening colonoscopy from October 2019 to October 2020 were included in this study. Large intestinal samples (ascending colon, descending colon, sigmoid colon, and rectum) were aspirated by colonoscopy. Rectal swabs were collected before colonoscopy, and stool samples were collected before patients began colonoscopy preparation. All samples were subjected to 16S ribosomal RNA gene sequencing. We identified differences in the number of phylum-level operational taxonomic units among large intestinal samples, rectal swabs, and stool. Five major phyla were detected in all samples (Firmicutes, Bacteroides, Proteobacteria, Actinobacteria, Fusobacteria), although their relative abundances varied. Notably, we found that the microbial compositions of rectal swabs were most similar to those of the sigmoid colon and rectum, whereas the microbiota in stool were relatively different than those from the large intestine and rectal swabs. Our results reveal the existence of microbial heterogeneity within different large intestinal compartments and further suggest that rectal swabs are an acceptable and practical tool for gut microbiota analysis. KEY POINTS: • Our findings highlight local microbiome variations within different regions of the large intestine. • Stool samples do not appear to fully recapitulate the gut microbiome. • Our data from a large population-based cohort indicate that rectal swabs can be used to study the gut microbiome.