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Population Shift

Newly diagnosed Crohn’s disease patients show rise in bad, drop in good, intestinal microbes

<i>Escherichia coli</i> are found in the human intestine.<br/>Photo: iStock.com

The intestinal microbial populations in patients newly diagnosed with Crohn’s disease have been found to differ from those in people free of inflammatory bowel disease, says research from a multi-institutional study led by investigators from HMS, Massachusetts General Hospital, and the Broad Institute. Crohn’s patients, according to their paper in the March 12 issue of Cell Host and Microbe, have increased levels of the harmful bacteria and reduced levels of the beneficial bacteria normally found in a healthy gastrointestinal tract.

Several studies have suggested that the excessive immune response that characterizes Crohn’s may be linked to an imbalance in the normal microbial population, but the exact relationship has not been clear. The current study analyzes data from a tool designed to investigate microbial, genetic, and other factors. Participants were children newly diagnosed with Crohn’s or other inflammatory bowel diseases as well as control participants with noninflammatory gastrointestinal conditions.

Advanced sequencing of the microbiome—the genome of the entire microbial population—in tissue samples taken from sites at the beginning and the end of the large intestine showed that, compared with samples from controls, Crohn’s patients showed an abnormal increase in the proportion of inflammatory organisms and a drop in noninflammatory and beneficial species. The imbalance was even greater in patients with severe symptoms and in those whose tissue had markers of inflammatory activity. 

None of the Crohn’s patients had received treatment at the time of sampling. Antibiotics are often prescribed for symptoms suggestive of Crohn’s before a diagnosis is made, and in participants who happened to be taking antibiotics at the time samples were taken, the microbial imbalance was even more pronounced, says senior author Ramnik Xavier, the HMS Kurt J. Isselbacher Professor of Medicine in the Field of Gastroenterology at Mass General and director of the MGH Center for the Study of Inflammatory Bowel Disease.



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