When bacteria-killing viruses take over, it’s bad news for the gut

People with inflammatory bowel diseases carry more of some of these viruses, less good bacteria

Virome shapes graphic

VIRUS GUT-PUNCH  Bacteria-infecting viruses called bacteriophages may kill friendly bacteria in the gut, causing inflammation and disease, a new study shows.

J.M. Norman et al./Cell 2015 (graphical abstract)

When it comes to inflammatory bowel disease, the enemy of my friends is my enemy, too, a new study suggests.

Bacteriophages — viruses that infect and kill bacteria — are more diverse in people with Crohn’s disease or ulcerative colitis. Herbert “Skip” Virgin, an immunologist at Washington University in St. Louis, and colleagues report the finding online January 22 in Cell. In particular, Caudovirales bacteriophages were more diverse in people with the diseases than in healthy people living in the same households, the researchers found.

The viruses may kill friendly bacteria in the intestines, leading to inflammation and disease. Scientists already knew that people with Crohn’s and colitis tend to have fewer types of beneficial bacteria in their gut microbiomes. The microbiome is the complete collection of bacteria, viruses, fungi and other microorganisms that live in or on the body. What researchers hadn’t understood is why the bacterial diversity decreased.

The new results suggest some viruses may damage health not by infecting human cells, but by altering the microbial mixes in the body. The findings may also explain why fecal transplants from healthy people generally haven’t cured inflammatory bowel diseases; lingering viruses may destroy newly introduced bacteria before they can do the patient any good.

Tina Hesman Saey

Tina Hesman Saey is the senior staff writer and reports on molecular biology. She has a Ph.D. in molecular genetics from Washington University in St. Louis and a master’s degree in science journalism from Boston University.

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