title: Role of colonic microbiota in colorectal carcinogenesis: a systematic review.
abstract: OBJECTIVE
  The human colonic mucosa is populated by a wide range of microorganisms, usually in a symbiotic relation with the host. Sometimes this balance is lost and a state of dysbiosis arises, exposing the colon to different metabolic and inflammatory stimuli (according to the microbiota's changing profile). Recent findings lead to hypothesize that this unbalance may create a subclinical pro-inflammatory state that increases DNA mutations and, therefore, colorectal carcinogenesis. In this article we aim to systematically review the scientific evidence regarding colonic microbiota and its role in colorectal carcinogenesis.
  
  
  METHODS
  Systematic review of PubMed searching results for original articles studying microbiota and colorectal cancer until November 2014.
  
  
  RESULTS
  Thirty-one original articles studied the role of colon microbiota in colorectal carcinoma including both human and animal studies. Different and heterogeneous methods were used and different bacteria were considered. Nevertheless, some bacteria are consistently augmented (such as Fusobacteria, Alistipes, Porphyromonadaceae, Coriobacteridae, Staphylococcaceae, Akkermansia spp. and Methanobacteriales), while other are constantly diminished in colorectal cancer (such as Bifidobacterium, Lactobacillus, Ruminococcus, Faecalibacterium spp., Roseburia, and Treponema). Moreover, bacteria metabolites amino acids are increased and butyrate is decreased throughout colonic carcinogenesis.
  
  
  CONCLUSIONS
  Conclusive evidence shows that colorectal carcinogenesis is associated with microbial dysbiosis. This information may be used to create new prophylactic, diagnostic and therapeutic strategies for colorectal cancer.
authors.affiliation: Physiology and Cardiothoracic Surgery, Faculty of Medicine, University of Porto, Portugal.
authors.forename: Marta
authors.initials: M
authors.lastname: Borges-Canha
authors.affiliation: University of Porto. Portugal. .
authors.forename: José Pedro
authors.initials: JP
authors.lastname: Portela-Cidade
authors.affiliation: Portuguese Oncology Institute. Porto, Portugal. .
authors.forename: Mário
authors.initials: M
authors.lastname: Dinis-Ribeiro
authors.affiliation: University of Porto. Portugal. .
authors.forename: Adelino F
authors.initials: AF
authors.lastname: Leite-Moreira
authors.affiliation: University of Porto. Portugal. .
authors.forename: Pedro
authors.initials: P
authors.lastname: Pimentel-Nunes
mesh_terms: D000818:Animals; D063646:Carcinogenesis; D003106:Colon / Q000382:microbiology*; D015179:Colorectal Neoplasms / Q000382:microbiology*; D064806:Dysbiosis; D006801:Humans; D064307:Microbiota