Scientists Discover Exactly How Cranberry Juice Fights Infections

For decades, the idea that drinking cranberry juice could prevent or treat urinary tract infections was greeted with doubt and sometimes even sarcasm by doctors who considered this an "old wives' tale". But in recent years, studies have shown that cranberry juice does exactly what countless grandmas and herbalists said it does. It wards off infections. But how?

Now comes word that researchers at Worcester Polytechnic Institute (WPI) have the answer. Cranberry juice creates what the scientists call an "energy barrier" that has the amazing power to prevent disease-causing microorganisms from starting an infection. This barrier changes the thermodynamic properties of infection-causing germs in the urinary tract. Simply put, the bacteria are then unable to hook onto cells and cause illness.

The study looked at two varieties of E. coli bacteria -- one with projections known as fimbriae which are believed to be used by bacteria to latch into cells and one without the hair-like appendages. The bacteria with fimbriae are found on many virulent bacteria, including those that cause painful urinary tract infections.

Both varieties were exposed to different concentrations of cranberry juice. The research team, headed by Terri Camesano, associate professor of chemical engineering at WPI, and a team of graduate students, including PhD candidate Yatao Liu, found that even at low concentrations the fruit juice made it difficult for the illness-causing bacteria to attach to cells. The scientists' conclusions, recently published in the science journal Colloids and Surfaces, strongly indicate that cranberry juice repels bacteria with fimbriae. The juice had had little if any effect on E. coli bacteria without the hair-like projections, suggesting that something in the juice interacts directly only on the "bad bacteria" that has tentacle-like fimbriae.

"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 in a statement for the press. "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."

She also said that to take advantage of the antibacterial benefits of cranberry, it's a good idea to consume cranberry juice regularly –- even daily.

In fact, drinking cranberry juice might do more than help prevent painful urinary tract infections. The Mayo Clinic is currently enrolling research subjects in a study to see if the fruit juice can help prevent cardiovascular disease. Previous studies have shown that cranberries can lower "bad" cholesterol levels, and help reduce the risk of gum disease, stomach ulcers and cancer.