Cranberry Juice Shows Promise as Alternative to Antibiotics

New research has greatly increased our understanding of how cranberry juice prevents urinary tract and kidney infections.

A series of studies led by Terri Camesano from Worcester Polytechnic Institute, the latest of which were presented September 19, 2006 at the annual meeting of the American Chemical Society in San Francisco, show that compounds in cranberry juice have the capacity to actually change E. colibacteria-even strains that have become resistant to conventional treatment-in ways that render them unable to initiate an infection. E. coli, a class of microorganisms responsible for a wide variety of human illnesses ranging from urinary tract and kidney infections to gastroenteritis to tooth decay, are changed in several ways by a group of tannins (called proanthocyanidins) found primarily in cranberries. Each one of these changes can prevent the bacteria from adhering to cells in the body, a necessary first step in any infection.

Cranberry proanthocyanidins:

• Alter E. coli’s cell membranes
• Prevent the bacteria from making contact with cells or attaching to them even if they somehow manage to get close enough
• Change the shape of E.coli from rods to spheres
• Disrupt bacterial communication

Alter E. coli Cell Membranes

In research published February 2006 in Biotechnology and Bioengineering, Camesano showed that exposure to 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 urinary tract infections to become compressed. Since its fimbriae are what allow the bacteria to bind tightly to the lining of the urinary tract, compressing them greatly reduces E. coli’s ability to remain in place long enough to launch an infection.

Prevent E. coli from Making Contact

In research published in August 2006 in Colloids and Surfaces, B. Biointerfaces Camesano found that chemical changes caused by cranberry juice also create an energy barrier that prevents the bacteria from getting close enough to the urinary tract lining to try to adhere in the first place.

Change E. coli’s Shape and Activity

Camesano’s latest work reveals that cranberry juice can transform E. coli in even more radical ways, which have never before been observed. When the bacteria were grown in solutions containing various concentrations of either cranberry juice or cranberry tannins, E. coli, which is normally a gram-negative rod-shaped bacterium, became spherical and started behaving like gram-positive bacteria. Since gram-negative and gram-positive bacteria differ primarily in the structure of their cell membranes, these results suggest that cranberry tannins actually alter E. coli’s membrane.

The research Camesano presented at the ACS meeting also included yet another, more preliminary finding: when exposed to cranberry juice, E. coli appear to lose their ability to secrete indole, a molecule involved in a form of bacterial communication called quorum sensing, which is used by E. colito determine when sufficient bacteria are present at a location to stage a successful infection attack.

“We are beginning to get a picture of cranberry juice and, in particular, the tannins found in cranberries, as potentially potent antibacterial agents,” Camesano said. “These results are surprising and intriguing, particularly given the increasing concern about the growing resistance of certain disease-causing bacteria to antibiotics.” For most of these effects, the higher the concentration of either cranberry juice or tannins, the greater their impact on E. coli, suggesting that whole cranberry products and juice that has not been highly diluted may have the greatest health effects.