image: Wisconsin State Cranberry Grower’s Association
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Cranberries may be too tart for some, but they could help your health. As this ScienCentral News video explains, scientists have discovered why some compounds in cranberries are so powerful against the bacteria that cause millions of urinary tract infections a year.
Tart and Healing
Cranberries and cranberry juice are the home-remedy of choice for urinary-tract infections, and their healing power can be traced back to Native Americans, who used the fruit medicinally for centuries as a treatment for arrow wounds.
It's not just folklore: Scientific studies have confirmed cranberry's health benefits for urinary tract infections. But what's puzzling is scientists have not been able to determine the specific mechanism behind this effect, or how and why it works. (In 1923 scientists proposed that the acidity of cranberries produces an antibacterial effect in the body, but these theories were later disproven.)
So Worcester Polytechnic Institute chemical engineer Terri Camesano assembled a team to study the effects of the chemical compounds in cranberries at the molecular level. In multiple experiments, they pitted cranberry juice and cranberry compounds against E. coli. They worked with the E. coli HB101 strain, which is one of the many different bacteria that can cause urinary tract infections. Under the microscope, Camesano's team saw that a chemical in cranberries was causing changes in the bacteria.
When E. Coli grows in the presence of cranberry juice for long periods of time, the shape of the bacteria changes. image: Worcester Polytechnic Institute
"When we actually grow E. coli in the presence of cranberry juice for long periods of time, we see that the whole shape of the E. coli cell seems to change. It's a rod shape initially and then it becomes more like a spherical cell," she says. This change has never been seen before in E. coli, and means that the cranberries are somehow changing the membrane or skin of the bacteria.
The trick is that these changes in the bacteria also caused them to be repelled by human cells. By studying the electrical forces between E. coli and the cells that line the urinary tract, Camesano found that cranberry juice created an energy barrier. "You can envision how there's a force field around the E. coli bacteria that somehow prevents it from being able to attach to cells in the urinary tract," she says.
Previous research by Camesano's team found that cranberries also have an effect on little hairs that are on the surface of E. coli. "We immediately saw that these molecules, these little hairs change in that [they] became completely collapsed on the surface. Once that happened the E. coli could no longer form an adhesion, could no longer bond to the cells in the urinary tract," Camesano says.
Camesano conducted several of these experiments with proanthocyanidins, a key component to cranberry's power against urinary tract infections. These chemicals are a type of tannin, which has been found to have multiple nutritional benefits in tea, wine, and pomegranate.
Camesano hopes that these discoveries can lead to better treatment options for urinary tract infections, which affect nearly 8 million people per year in the United States. Urinary tract infections occur when bacteria move up the urinary tract, and patients may feel a burning sensation when trying to urinate. The condition is common, especially in females, children, and the elderly.
Camesano says that while some see urinary tract infections as simply an occasional nuisance, for some, the infection can be serious. "There are people with recurrent urinary tract infections that even if they continue to take antibiotics, they can't seem to get rid of the infection," she says.
By studying the mechanisms behind cranberry's protective benefits, Camesano says that we can develop better treatment options for bacteria in general. "E. coli are really in some ways not that different from lots of other bacteria, and maybe we could start to think about using cranberry for other types of bacterial infections."
And, as antibiotics develop resistance over time, Camesano says that it's important to look to the cranberry for further research. "So if we can get some sort of treatment for patients that comes from a non-antibiotic source, especially something that is already known to be safe, I think that has a lot of health implications."
Camesano says other studies have found that these compounds are inside blueberries as well, but more research is needed to see if blueberries are as effective against urinary tract infections. For cranberry juice, benefits have been seen in clinical studies with cranberry juice cocktail, cranberry mixed with water, cranberry-lingonberry concentrate, pure cranberry juice, and even cranberry capsules, according to Camesano's previous study.