Common early-life exposure of the colorectal epithelium to the microbiome-derived mutagen colibactin

Colibactin is a mutagen produced by bacterial strains in the colorectal microbiomes of some healthy people. It generates somatic mutations characterised by the mutational signatures SBS88 and ID18 in normal human colorectal epithelial cells in vivo. Increasing prevalence of colibactin mutagenesis during the 20th century is hypothesised to have caused recent international increases in early-onset colorectal cancer incidence. Here, we establish the early-life prevalence, timing, mutation burdens and distribution through the colon of colibactin mutagenesis by sequencing normal colorectal epithelial cell genomes to detect SBS88 and ID18 in children and adolescents from the UK and Denmark biopsied between 2016 and 2024. Colibactin mutagenesis was found in ~40% individuals. It starts soon after birth and often ceases by age five years, although some children show longer exposures. Mutation burdens are higher in the left than right colon and show substantial variation between exposed individuals, in some causing >100-fold increases in total mutation loads compared to unexposed children of the same age. Therefore, colorectal mutagenesis by colibactin is currently common in some populations, occurs during early childhood and can produce markedly elevated somatic mutation burdens. The future public health implications of this widespread mutagen exposure will depend on clarification of its role in colorectal cancer causation.

• 12/03/2026
• 1 sample
• DAC: EGAC00001000000
• Technology: Illumina NovaSeq 6000