Microbes in mouse guts can interfere with infection responses by changing the expression of small RNAs that regulate some genes.

Cristel Archambaud and Pascale Cossart at the Pasteur Institute in Paris and their colleagues looked at the expression of microRNA molecules in the small intestines of mice before and after infection with Listeria monocytogenes, a food-borne pathogen. They found reduced expression of six microRNAs after the infection in normal mice, but no decrease was seen for five of the microRNAs in mice without gut microbes, suggesting that the microbiota was responsible for this effect.

The findings suggest that gut microbes regulate the expression of protein-coding genes that are controlled by the microRNAs during infection.

mBio 4, e00707-13 (2013)