Mucosal Adherent Bacteria and Colorectal Adenomas

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The relationship between commensal intestinal bacteria and colorectal adenomas is unclear because the human bowel is colonized by complex and diverse bacterial communities. However, recent findings from the University of North Carolina at Chapel Hill School of Medicine and published in the journal Gut Microbes suggest that alterations in bacterial community composition associated with adenomas may contribute to colorectal cancer etiology.

The study led by Temitope O. Keku, PhD, Research Associate Professor of Medicine, UNC Center for Gastrointestinal Biology and Disease, evaluated adherent bacteria in normal colonic mucosa isolated from 21 adenoma and 23 nonadenoma subjects. Terminal restriction fragment length polymorphism, clone sequencing and fluorescent in situ hybridization analysis of the 16S rRNA genes were among the molecular methods used to characterize adherent bacteria. In all, 335 clones were sequenced and processed. The most dominant phyla were Firmicutes (62%), Bacteroidetes (26%), and Proteobacteria (11%).

“We observed significantly higher abundance of Proteobacteria (P < .05) and lower abundance of Bacteroidetes (P < .05) in cases compared to controls,” the authors state. “Cases had higher bacterial diversity and richness than controls.” In particular, Proteobacteria was in higher abundance in cases than in controls.

It is still not clear whether alterations in bacterial composition cause adenomas, or, conversely, if adenomas cause this altered balance. Keku plans to conduct more studies, including testing whether certain groups of bacteria promote cancer growth in animal models. The researcher is expanding the study to analyze samples from 600 patients using next-generation sequencing technology “to provide deeper coverage of bacterial communities.”

The ultimate goal may be to determine if the differences in bacterial populations found in the mucosa lining the colon also exist within the luminal fraction. If so, it could mean less invasive screening for cancer and more cancers being caught earlier, when survival rates are higher.

“Our findings suggest that adherent bacteria may be significant players in the development of adenomas and colorectal cancer,” the authors state. “Extension of these findings could lead to strategies to manipulate the microbiota to prevent colorectal adenomas and cancer as well as to identify individuals at high risk.” See: Shen, et al, Gut Microbes, May/June 2010.