Gut Microbial Dysbiosis Induced Exacerbations Influence the Progression of Colorectal Cancer

Colorectal cancer (CRC) is second most deadly and third most commonly diagnosed cancer in the world. CRC cases have been increasing lately with a shift to fast food diets, unhealthy lifestyles and other environmental conditions. The gut microbiota thriving on dietary fibres and worn off mucus layers plays a decisive role in the homeostasis of the gut. In dysbiosis, this consortium of commensal microbes is replaced by harmful microbes, rather the pathogens leading to catastrophic outcomes with respect to the individual’s well-being, like chronic inflammation, interference in cellular mechanisms, promotion of tumour micro-environments, induction of prooncogenic immunity pathways, etc. A number of microorganisms are known to participate in tumorigenesis, working as ‘driver’ or ‘passenger’ bacteria with resultant oncogenic outcomes. Organisms like Bacillus fragilis, Porphyromonas gingivalis, Fusobacterium nucleatum, Streptococcus gallolyticus, collagenolytic Enterococcus faecalis, Peptostreptococcus anaerobius, E. coli and others have the ability to induce proinflammatory genes and precancerous precursors modulating the immune system and the stromal cells to support the growth of tumour. Mechanisms of these organisms participating in tumour growth, promotion and metastasis are mentioned and briefed about in this review. In most cases, the presence of these microbes is observed only after the tumour has already set in or in pre-cancerous stages, generally making the revival of the commensal population difficult to recolonise. Every individual has unique resident microbial footprint, showing virulence in one and not in another. Hence attempts should be made to maintain a diet rich in dietary fibres with a healthy lifestyle to avoid dysbiosis and further complications.