Tumour-associated and non-tumour-associated microbiota: Addendum.

In a recent study we reported that tissue-associated microbial Co-abundance Groups (CAGs) were differentially associated with colorectal cancer (CRC). Two of the CAGs, which we named Pathogen CAG and Prevotella CAG, were correlated with a gene expression signature indicative of a TH17 response. A TH17 response has been associated with decreased survival in patients with CRC, and members of the Pathogen CAG such as Fusobacterium nucleatum, Escherichia coli and Bacteroides fragilis have been repeatedly reported to be associated with CRC-development. Thus we hypothesized that the abundance of these CAGs may be associated with poor survival. In this Addendum we extend our analysis of the at-surgery microbiota to microbiota profiles obtained after surgery for CRC which we analyzed in the context of survival data for patients with CRC. Surprisingly we found that high tissue-associated abundance of the previously defined Prevotella- and Pathogen-CAGs at surgery was associated with longer survival. Furthermore, we detected an association of the Bacteroidetes CAG in pre-surgery faecal microbiota with stability of the microbiota after surgery.