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Patients with familial adenomatous polyposis harbor colonic biofilms containing tumorigenic bacteria.

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Dejea et al., Science 359, 592–597 (2018) 2 February 2018.

COMMENT: Some Escherichia coli and Bacteroides fragilis that produce oncotoxins and form biofilms at he colon mucosa could be related with colon cancer. Escherichia coli and Bacteroides fragilis are abundant bacteria in human gut, but there are special strains of these bacteria that produce oncotoxins. In this work the authors study the impact of 2 specific strains in familial adenomatous polyposis:

  • Escherichia coli producing the oncotoxin called colibactin (clbB)
  • Bacteroides fragilis producing the secreted oncotoxin encoded by bft gene

The relationship with tumorigenicity is only observed when the 2 strains are detected together forming biofilms at the colon mucosa as if the biofilm structure would be the refuge for cancerous bacteria.

Familial adenomatous polyposis (FAP) causes benign polyps along the colon. If left untreated, FAP leads to a high incidence of colon cancer. To understand how polyps influence tumor formation, Dejea et al. examined the colonic mucosa of FAP patients. They discovered biofilms containing the carcinogenic versions of the bacterial species Escherichia coli and Bacteroides fragilis. Colon tissue from FAP patients exhibited greater expression of two bacterial genes that produce secreted oncotoxins. Studies in mice showed that specific bacteria could work together to induce colon inflammation and tumor formation.

Cocolonization with these 2 carcinogenic strains was found in more than 50% of FAP patients  and only in 25% of controls. The authors suggest that the cooperative tumor induction steps could be:

  • mucus degradation, increased E. coli adherence and epithelial cell DNA damage by

colibactin  at the colon mucosa

  • IL-17 induction by enterotoxigenic Bacteroides fragilis increased by colibactin + E. coli cocolonization

The authors also suggest the potential application of the analysis of coexpression of bft and clbB in screening for colon cancer prevention

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Raquel Tobes