Impact of bacterial infection and intestinal microbiome on colorectal cancer development

Abstract

Accumulating evidence suggests that intestinal bacteria play an important role in the pathogenesis of colorectal cancer (CRC). Due to the complexity of the intestinal microbiome, identification of the specific causative microbial agents in CRC remains challenging, and the search for the causative microbial agents is intense. However, whether bacteria or their products can induce inflammation that results in tumorigenesis or directly causes CRC in humans is still not clear. This review will mainly focus on the progress of bacterial infection and CRC, and introduce the microbial contribution to the hallmarks of cancer. This article uses Salmonella and its chronic infection as an example to investigate a single pathogen and its role in the development of CRC, based on laboratory and epidemiological evidence. The bacterial infection leads to an altered intestinal microbiome. The review also discusses the dysfunction of the microbiome and the mechanism of host-microbial interactions, for example, bacterial virulence factors, key signaling pathways in the host, and microbial post-translational modifications in the tumorigenesis. Colonic carcinogenesis involves a progressive accumulation of mutations in a genetically susceptible host leading to cellular autonomy. Moving forward, more human data are needed to confirm the direct roles of bacterial infection in CRC development. Insights into the inhibiting infection will help to prevent cancer and develop strategies to restore the balance between host and microorganisms.

Figure 1

Microbial contribution to the progression of CRC. Bacterial factors manipulate the host signaling pathways, including APC/beta-catenin, p53, and other inflammatory responses, thus contributing to all steps of colon tumorigenesis, including initiation, promotion, progression, and metastasis. APC: Adenomatous polyposis coil; Cox-2: Cyclooxygenase-2; CRC: Colorectal cancer; IL-6: Interleukin 6; TNF: Tumor necrosis factor; TGFβR: Transforming growth factor-β receptor.