A typical gut bacterium, which can spread throughout the body and cause a serious infection, resists natural immune defenses and antibiotics by strengthening its protective outer layer, known as the cell envelope, according to a new study by Weill researchers Cornell Medicine. The discovery suggests possible new ways to target these bacterial infections.

The research illuminates some of the underlying changes that can occur when populations of Enterococcus faecalis (E. faecalis) moves through the epithelial cells that line the gut and escapes to reach other areas of the body.

“Systemic infections with E. faecalis can be lethal because this microbe has a remarkable ability to adapt to diverse environments and resist treatments,” said lead researcher Dr. Diana K. Morales, assistant professor of microbiology and immunology in obstetrics and gynecology at Weill Cornell Medicine.

People at risk of developing these infections include those who take antibiotics or who have a compromised immune system, which makes it easier for E. faecalis to overgrow in the gut.

Understanding how E. faecalis leaves the gut and spreads could one day help scientists find small molecules to stop the extraintestinal spread of the bacterium, preventing dangerous infections.

Gut bacteria can cause a serious infection

How the bacterium can move out of the gut and into other organs has remained largely unexplored. However, the researchers noticed that there were two different populations of the same species of bacteria, Dr. Morales said. One population develops traits that allow it to pass through the gut barrier acquiring advantageous antimicrobial resistance, while the other stays put.

In a series of previous laboratory studies of the bacterium, researchers found that mobile E. faecalis produces molecules made of sugar chains called polysaccharides that allow the bacterium to aggregate, or clump.

“When they aggregate, these bacteria seem to develop an ability to move,” Dr. Morales said, according to EurekAlert.

In the current study, researchers, including lead author Dr. Yusibeska Ramos, research associate in obstetrics and gynecology, found that the mobile form of E. faecalis has a cell envelope that contains increased amounts of glycolipids, which are fat molecules linked to a carbohydrate.

How could the bacteria get out of the body?

Increased production of cell envelope glycolipids appears to help the bacterium resist extracellular stressors. These stressors include the antimicrobial agent daptomycin, a common treatment for yeast infection E. faecalisand β-defensins, small molecules that intestinal epithelial cells produce to ward off infection.

The researchers also found that genetic mutations that inhibit glycolipid production made ca E. faecalis to be more sensitive to these stress factors and reduced the bacteria’s ability to penetrate cell surfaces and move through intestinal epithelial cells.

The researchers’ next step is to evaluate additional models to confirm whether, in fact, the molecular pathways discovered in the current study are necessary for the bacteria to exit the gut.

The research was published in the journal mBio.

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