Bacteria in food can benefit intestinal health, researchers at the School of Medicine have shown.

The research results demonstrate a mechanism by which bacterial cultures in foods such as yogurt and kimchi have beneficial effects on intestinal health.

These insights could also guide improved treatments for intestinal diseases, such as necrotizing enterocolitis in premature babies or intestinal injury in critically ill adults.

The laboratories of Andrew Neish and Asma Nusrat, both professors of pathology and laboratory medicine, teamed up for the study, published this week in the Proceedings of the National Academy of Sciences Early Edition.  The paper's co-first authors are postdoctoral fellow Philip Swanson and associate research professor Amrita Kumar.

"It's been known for years that probiotic bacteria can have these kinds of helpful effects, but it wasn't really clear how this worked," Neish says. "We've identified one example, among many, of how certain kinds of bacteria have specific biochemical functions in the body."

Recent research has shown that the bacteria in our intestines influence our metabolism and immune systems. An imbalance in the proportions of harmful and beneficial bacteria seems to over-activate immune cells in the intestines, driving inflammatory bowel disease.

Cells that line the intestine live in close contact with bacteria and normally form a barrier that keeps bacteria away from other organs. They can repair small gaps in the barrier, which breaks down in intestinal diseases, by moving into the gaps.

Using a fluorescent dye that is sensitive to reactive oxygen species (ROS), the researchers showed that intestinal epithelial cells produce ROS internally when in contact with Lactobacillus rhamnosus.

Lactobacillus rhamnosus, a species of bacteria found naturally in human intestines and often used as a probiotic, is a relative of other kinds of Lactobacillus bacteria found in fermented foods.

Antioxidants that mop up ROS prevent the bacteria from promoting wound healing in the laboratory, the researchers showed. Neish says his team's finding suggests that large amounts of antioxidants by humans could interfere with the ability of bacteria to promote intestinal healing.

Oxidative stress, or an imbalance of reactive oxygen species throughout the body, has been linked to diseases such as heart disease and stroke. However, scientists have learned in recent years that cells can also use reactive oxygen species in a controlled, local way to send signals needed for normal functions.

Neish says his team is working to determine which part of the bacteria is responsible for inducing cells to produce ROS. Once identified, this component could be used to encourage intestinal healing in situations where contact with large amounts of live bacteria might be dangerous, such as in premature babies or critically ill adults.

The research was supported by the National Institutes of Health.

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