The research is published in the March 2013 issue of the journal Infection and Immunity.

The reduced diversity of microbiota wrought by antibiotics "allow[s] VRE to invade and thrive in the intestine, suggesting that bacterial species that are wiped out by antibiotics are key to preventing colonization by VRE," says first author Carles Ubeda of the Centro Superior de Investigacion en Salud Publica, Valencia, Spain. "We hypothesized that repopulating the mice' intestines with the missing bacteria would promote clearance of the VRE."

In the study, the researchers treated mice with antibiotics. They then gave the mice fecal transplants from untreated mice, or aerobic or anaerobic cultures from the fecal transplants. Following the latter treatments, mice receiving the fecal transplant or the anaerobic culture were able to clear the VRE, while those receiving the aerobic culture failed to do so. The researchers compared the microbiota in each group. The big difference: the mice that had cleared the VRE contained bacteria from the anaerobic genus, Barnesiella, while those that had failed to clear the VRE did not.

The researchers then analyzed the fecal microbiota from human patients who had received bone marrow transplants, who were at high risk of being colonized by vancomycin-resistant enterococci. "The presence of Barnesiella in fecal samples was associated with protection against VRE, suggesting that in humans, Barnesiella may also confer protection against dense VRE colonization," says Ubeda.

"The findings could be very useful for development of novel probiotics," says Ubeda. Additionally, "scientifically, this is a major finding that will help us to understand how the microbiota confer resistance against intestinal colonization by pathogens, an important question that remains incompletely answered."