Table 2.

Microbes Associated With Increased or Reduced Risk of CRC

Microbe	Epidemiologic Evidence	Potential mechanisms	References
Associated with higher risk of CRC
Fusobacterium nucleatum	Enriched tumor tissue; higher fecal abundance in patients with colorectal neoplasia than controls; associated with advanced cancer stage, lower infiltration by T cells, higher risk of recurrence, and poorer patient survival; correlated with the molecular characteristics of the serrated pathway.	Promotion of a tumor-permissive microenvironment through recruitment of myeloidderived suppressor cells and inhibition of antitumor defense by NK or T cells; modulation of Ecadherin/β-catenin.	21, 22, 140, 219
Enterotoxigenic Bacteroides fragilis (ETBF)	Enriched in tumor tissue and fecal samples of CRC patients; associated with advanced cancer stage and proximal colon tumor.	DNA damage	40, 220, 221
pks+ Escherichia coli	More frequently detected in individuals with than without CRC, more frequently in tumors than in normal flanking tissue, and more frequently in late-stage tumors than in early-stage tumors.	Promotion of intestinal inflammation	49, 222
Associated with lower risk of CRC
SCFA-producing bacteria	Lower abundance in CRC patients than bacteria controls; higher abundance in Native Americans with a low CRC incidence; associated with improved immune response and better metabolic parameters.	Metabolic and immune modulation of SCFAs that protects against CRC.	124, 128, 223