Cranberries: A Natural Antibiotic?

The sweet and tangy side dish to most Thanksgiving meals, cranberry sauce, may be a major lifesaver as a natural antibiotic, according to researchers.

Researchers at the Worcester Polytechnic Institute found compounds in cranberries that can alter E. coli bacteria, responsible for human illnesses from kidney infections to gastroenteritis to tooth decay, making them unable to develop infection.

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The research shows there are biochemical and biophysical mechanisms in cranberries and cranberry juice, which produce infection-fighting benefits including the ability of cranberry juice to prevent urinary tract infections.

The mechanism by which cranberry juice fights these infections is not clear, but scientists believe there are compounds in the juice that prevent bacteria from lining the urinary tract.

Terri Camesano, associate professor of chemical engineering at WPI, and her students used an atomic force microscope and other tools to study how the grouping of tannins found primarily in cranberries interacted with bacteria at a molecular level.

Their study found that the cranberry compounds prevented E. coli from adhering to cells in the body, one of the first steps in infection, in the following ways:

— The chemical changes caused by cranberry juice create an energy barrier that keeps the bacteria from getting close to the urinary tract lining.

— Direct measurements show that the adhesive forces between E. coli and cells of the urinary tract are greatly reduced when at least a 5 percent solution of cranberry juice cocktail is present.

— Cranberry juice causes tiny tendrils (known as fimbriae) on the surface of the type of E. coli bacteria responsible for the most serious types of UTIs to become compressed, reducing the bacteria’s ability to latch onto the lining of the urinary tract.

— E. coli grown in cranberry juice or the isolated PACs are unable to form biofilms. Biofilms, clusters containing high concentrations of bacteria, are required for infections to develop. Biofilms are the source of infections associated with indwelling catheters and other biomedical devices.

— When E. coli are cultured over extended periods in solutions containing various concentrations of either cranberry juice or PACs, their cell membranes undergo changes that hinder the bacteria’s ability to attach to cells of the urinary tract.

The team at WPI also noticed that cranberry juice also inhibits E. coli from producing IAA, a molecule that leads to quorum sensing, where bacteria sense other populations of bacteria and develop into infection. By preventing bacteria from producing IAA, cranberries compounds may ultimately prevent infection, according to the research.

Camesano’s continued work will also assess the minimum effective dose of cranberry juice or tannins and the frequency of intake necessary to ward off infections. In addition, she is studying whether the urine of patients who have consumed cranberry juice still contain anti-adhesive properties.