A 2023 paper combined results of two clinical trials focused on large intestine microbiota:

“Our current understanding of the gut microbiome places it at the center of multiple physiological processes, and establishes its relevance to many facets of health and disease. Microbiome databases are based upon stool samples or invasively-acquired colon samples obtained during procedures such as colonoscopy.

We present data from two prospective clinical studies describing significant differences between the stool microbiome and inner-colonic microbiome collected during FDA-cleared defecation-inducing, gravity-fed, and high-volume colonic lavage. We examined several microbiome characteristics, including microbial diversity, community differential abundance, and composition of biosynthetic gene clusters (BGCs).

BGCs are locally clustered groups of two or more genes that encode a biosynthetic pathway that produces a secondary metabolite:

• 6% of identified BGCs were common to stool and pooled inner-colonic effluent samples, 25% were expressed only in stool, and 69% were unique to effluent samples.
• When effluent-specific BGCs were divided according to colon areas, 25% were found in Effluent-1 (left descending colon), 21% in Effluent-2 (transverse colon), and 11% in Effluent-3 (right ascending colon).

Taxonomic and phylogenetic differences between inner-colonic effluent and stool samples increased gradually when approaching the proximal colon and small intestine:

• Comparing the left colon to stool showed that 22 species were significantly enriched while only five species were significantly more abundant in stool.
• A comparison between the transverse colon and stool revealed 76 species that were significantly more differentially abundant, while stool had 10 differentially abundant species.
• The most significant differentially abundant species were found by comparing the right colon (closest to the small intestine) to stool, with 96 species differently enriched while stool had 20 species significantly enriched.

Individuals are far more distinct in their inner-colonic microbial community than in their stool samples. Microbiota are relatively similar across patients when examining stool samples, while expression of rare microbial strains is more specific to each individual.

Analyzing both stool and inner-colonic effluents can provide more information on the gut microbiome.”

https://www.cell.com/heliyon/fulltext/S2405-8440(23)00809-5 “The gut microbiome–Does stool represent right?”

Continued in Part 2.