69 Colorectal cancer (CRC) remains a leading cause of cancer-related deaths globally, but emerging research highlights the significant role of gut microbiota in its development and progression. Recent studies have delved into the intricate relationship between gut microbiota and CRC, revealing that alterations in the gut microbiome, often termed “dysbiosis”, play a crucial role in the pathogenesis of CRC. Dysbiosis, which is characterised by an imbalance in the microbial community, can result from using antibiotics, among other things. This imbalance has been linked to increased CRC risk, underscoring the importance of understanding these microbial shifts to develop better preventive and therapeutic strategies. The findings were published in the journal Nature Microbiology. Research over the past decade has generated extensive metagenomic data from CRC patients, showing that their gut microbiota composition significantly differs from that of healthy individuals. These studies have found certain types of bacteria that are more common in people with colorectal cancer. These include Fusobacterium nucleatum, Porphyromonas, Parvimonas, and Peptostreptococcus, among others. These bacteria are believed to contribute to the cancer’s development through various mechanisms, including inflammation, immune modulation, and direct genotoxic effects. Interestingly, these microbial shifts are not uniform across all CRC patients, indicating that individual variability plays a significant role. Factors such as diet, lifestyle, and genetic predispositions can influence the gut microbiome’s composition, adding layers of complexity to understanding CRC’s microbial aspect. Among the microorganisms implicated in CRC, several have been studied extensively for their potential roles in cancer initiation and progression. For instance, the bacterium Fusobacterium nucleatum has been found to be enriched in CRC tissues. It can promote cancer development by modulating the host’s immune response and directly interacting with cancer cells. Also, Escherichia coli strains that carry the polyketide synthase (pks) island can make colibactin, a genotoxin that causes DNA double-strand breaks and helps colorectal tumours grow. Other notable bacteria include Bacteroides fragilis, which produces a toxin that can trigger inflammation and promote cancer cell proliferation, and Streptococcus gallolyticus, which is associated with an increased risk of CRC due to its ability to induce chronic inflammation and cellular proliferation. These microorganisms highlight the diverse mechanisms through which the gut microbiota can influence CRC development. The exact mechanisms by which these microorganisms contribute to CRC are complex and multifaceted. One key pathway involves microbial metabolites, such as secondary bile acids (SBAs) and short-chain fatty acids (SCFAs), which can influence cellular processes in the colon. For example, certain SBAs have been found to promote cancer stem cell proliferation, while others like ursodeoxycholic acid, can inhibit tumour growth. SCFAs, produced through the fermentation of dietary fibres by gut bacteria, play critical roles in maintaining the epithelial barrier’s integrity and modulating the immune response. However, the depletion of butyrate-producing bacteria in CRC patients suggests a disruption in these protective mechanisms, contributing to the cancer’s progression. The growing understanding of the microbiota-CRC relationship opens new avenues for CRC prevention, diagnosis, and treatment. Current diagnostic tools, such as colonoscopy and faecal tests, have limitations, especially in detecting early-stage CRC or advanced adenomas. Incorporating microbial signatures into screening strategies could improve early detection and intervention. Preventive measures could also benefit from this research. For instance, dietary interventions to modulate gut microbiota composition, such as increasing fibre intake to boost SCFA production, show promise in reducing CRC risk. Moreover, targeting specific pathogenic bacteria through probiotics, antibiotics, or phage therapy could become viable strategies to prevent or treat CRC.