The potential role of Listeria monocytogenes in promoting colorectal adenocarcinoma tumorigenic process

Listeria monocytogenes is a foodborne pathogen, which can cause a severe illness, especially in people with a weakened immune system or comorbidities. The interactions between host and pathogens and between pathogens and tumor cells have been debated in recent years. However, it is still unclear how bacteria can interact with tumor cells, and if this interaction can affect tumor progression and therapy. In this study, we evaluated the involvement of L. monocytogenes in pre-neoplastic and colorectal cancer cell proliferation and tumorigenic potential. Our findings showed that the interaction between heat-killed L. monocytogenes and pre-neoplastic or colorectal cancer cells led to a proliferative induction; furthermore, by using a three-dimensional cell culture model, the obtained data indicated that L. monocytogenes was able to increase the tumorigenic potential of both pre-neoplastic and colorectal cancer cells. The observed effects were then confirmed as L. monocytogenes-specific, using Listeria innocua as negative control. Lastly, data suggested the Insulin Growth Factor 1 Receptor (IGF1R) cascade as one of the possible mechanisms involved in the effects induced by L. monocytogenes in the human colorectal adenocarcinoma cell line. These findings, although preliminary, suggest that the presence of pathogenic bacterial cells in the tumor niches may directly induce, increase, and stimulate tumor progression.