The news comes as welcome relief for those that suffer from UTIs, which each year affect eight million people, mostly women, the elderly and infants resulting in $1.6bn (€1.3bn) in health care costs.
Until now, scientists have not understood exactly how cranberry juice prevents UTIs and other bacterial infections, though they have suspected that compounds in the juice somehow prevent bacteria from adhering to the lining of the urinary tract.
The new findings reveal how the compounds interfere with adhesion at the molecular level.
The results of this new research by scientists at Worcester Polytechnic Institute (WPI) demonstrated that a group of tannins (called proanthocyanidins) found primarily in cranberries affect E. coli in three ways, all of which prevent the bacteria from adhering to cells in the body, a necessary first step in all infections.
Previous work by the team, led by Terri Camesano, associate professor of chemical engineering at WPI, and graduate students Yatao Liu and Paola Pinzon-Arango, showed that chemical changes caused by cranberry juice also created an energy barrier that keeps the bacteria from getting close to the urinary tract lining in the first place.
The new work, which will be presented on Sunday, Sept. 10, at the annual meeting of the American Chemical Society (ACS) in San Francisco showed that cranberry juice could transform E. coli bacteria in even more radical ways.
The researchers grew E. coli over extended periods in solutions containing various concentrations of either cranberry juice or tannins.
Over time, the normally rod-shaped bacteria became spherical - a transformation that has never before been observed in E. coli.
The E. coli bacteria, all of which fall into a class called gram-negative bacteria, began behaving like gram-positive bacteria - another never-before-seen phenomenon.
Since gram-negative and gram-positive bacteria differ primarily in the structure of their cell membranes, the results suggest that the tannins in cranberry juice can alter the membranes of E. coli.
A final, more preliminary result meeting suggests that E. coli bacteria exposed to cranberry juice appear to lose the ability to secrete indole, a molecule involved in a form of bacterial communication called quorum sensing. E. coli use quorum sensing to determine when there are enough bacteria present at a certain location to initiate a successful infection.
"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."