Gut Microbes and Colorectal Cancer | Second Genome

Colorectal cancer (CRC) is the second most common cause of death from cancer in the United States. Early diagnosis is important in successful treatment but detection requires regular screening through the use of colonoscopies in at-risk patients, an unpleasant and lengthy process for the patient. Research suggests that some species of gut bacteria, either acquired as an infection or naturally occurring in the gut microbiome, play a role in the pathogenesis of CRC but there is little clinical data to confirm the particular microbiome composition associated with CRC. An understanding of the CRC microbiome could provide useful information for the development of more efficient, effective, and patient-friendly diagnostic tools and treatments for CRC. In a paper recently published online in PLoS One, Dr. Julian Marchesi and colleagues go one step further towards this goal by providing a high-resolution map of the microbiome of CRC tumor tissue.

In the study, samples of tissue from primary colon tumors and from adjacent non-malignant tissue were removed during surgery in six patients with CRC. Interestingly the microbial communities present in the tumor tissue were significantly different from those present in the normal tissue. In general there were more Bacteriodetes and less Firmicutes in the tumor tissue than in the normal tissue. More specifically there was an overrepresentation of Coriobacteridae in the tumor tissue samples and an underrepresentation of Enterobacteriaceae including Citrobacter, Shigella, Cronobacter, and Salmonella. In addition to the differences between the two types of tissue there was no consistent presence of any potential pathogenic bacteria in the CRC tissue.

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The Coriobacteridae are considered to be gut commensal bacteria with probiotic features. Their enrichment in CRC tumor tissues suggests that as a result of the physiological and metabolic alterations that occur during the process of carcinogenesis certain bacterial species are able to thrive in the tumor microenvironment while others are not. In addition, some of the CRC ?passenger? bacteria have anti-tumorigenic and anti-carcinogenic properties which the authors argue may prevent rapid progression of the disease. In contrast the underrepresentation of some of the Endobacteriaceae in the tumor tissue compared to the normal tissue suggests that these bacteria may be a part of the intrinsic microbiome in CRC patients. In general Citrobacter, Shigella, Cronobacter, and Salmonella are pathogenic and are found only in low levels in the gut microbiome. The fact that they were detectable in higher levels in these patients may point to their involvement in the development of CRC. However, without a comprehensive understanding of what constitutes a healthy microbiome this idea is only a hypothesis.

In the future, further study of how the microbiome of CRC tissue changes as the disease progresses could be useful in the development of diagnostic tools, particularly if those changes can be detected in the fecal microbiome, and also perhaps in the development of therapeutic interventions.

About the author: Ruth Warre is a freelance scientific writer and editor currently living in Toronto. She writes on a variety of subjects from microbiomes to neuroscience, in a variety of mediums from blogs to peer-reviewed articles.

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Source: http://www.secondgenome.com/2011/09/gut-microbes-and-colorectal-cancer/

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