Cranberry juice has long been known to ward off urinary tract infections, but the exact mechanism of its action has not been well understood. Now, a new study by researchers at Worcester Polytechnic Institute (WPI) reveals that the juice changes the thermodynamic properties of bacteria in the urinary tract, creating an "energy barrier" that prevents microorganisms from getting close enough to latch onto cells and initiate an infection. The study, appearing in the journal Colloids and Surfaces: B, was conducted by WPI's Terri Camesano and Yatao Liu. They exposed two varieties of E. coli bacteria, one with hair-like projections known as fimbriae and one without, to different concentrations of cranberry juice. Fimbriae are present on a number of virulent bacteria, including those that cause urinary tract infections, and are believed to be used by bacteria to form strong bonds with cells.
For the fimbriaed bacteria, they found that even at low concentrations, cranberry juice altered two properties that serve as indicators of the ability of bacteria to attach to cells. With cranberry juice, bacterial attachment to urinary tract cells became increasingly unlikely.
But cranberry juice had no discernible effect on E. coli bacteria without fimbriae, suggesting that compounds in the juice may act directly on the molecular structure of the fimbriae themselves.
"Our results show that, at least for urinary tract infections, cranberry juice targets the right bacteria — those that cause disease — but has no effect on non-pathogenic organisms, suggesting that cranberry juice will not disrupt bacteria that are part of the normal flora in the gut," Camesano said. "We have also shown that this effect occurs at concentrations of cranberry juice that are comparable to levels we would expect to find in the urinary tract."
Camesano cautioned that while cranberry juice has potent effects on disease-causing bacteria, those effects are transitory. "When we take E. coli bacteria that have been treated with cranberry juice and place them in normal growth media, they regain the ability to adhere to urinary tract cells," she explained. "This suggests that to realize the antibacterial benefits of cranberry, one must consume cranberry juice regularly — perhaps daily."
For those watching calories, Camesano says other recent work in her lab has shown that the effects of regular cranberry juice cocktail and diet (sugar-free) cranberry juice are identical. "That's good news for people who do not like to consume a lot of sugary juice," she concluded.
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Source: Worcester Polytechnic Institute
