For Bacteroides spp., a significant difference between small cell GI lymphoma and IBD was observed in which compartments?

• A. In ileum only
• B. In colon only
• C. In the 3 combined ileal mucosal compartments ONLY (not colon)
• D. In both ileum and colon

Answer: (C)

Differences in gut microbiota between diseases can vary by tissue compartment, because the local environment and immune interactions shape which bacteria thrive. For Bacteroides spp., the ileal mucosa provides a distinct milieu with close contact to Peyer’s patches and a different immune and mucus landscape compared with the colon, so microbial signals that distinguish lymphoma from inflammatory bowel disease may be amplified there.

The finding here shows that when the three ileal mucosal compartments are analyzed together, there is a significant difference in Bacteroides abundance or composition between small cell GI lymphoma and IBD. This implies that the disease-specific microbial signal for Bacteroides is present across multiple ileal mucosal layers and only becomes detectable when these compartments are pooled, increasing statistical power. In contrast, the colon does not show this significant difference, so the compartments where the signal appears are restricted to the ileal mucosa, collectively.