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Nutrient - Urinary Tract Infections - How cranberries help fight bacterial infections

By Nutri People

Most people who have been unfortunate enough to suffer from urinary tract infections will probably have heard of the folk remedy of drinking cranberry juice to help prevent future infections. Traditionally, the highly acidic nature of cranberries was thought to cause acidification of the urine, creating an environment in which the bacteria that plague women with urinary tract infections cannot survive. However, recently, a team of researchers has shown that cranberry juice actually blocks the ability of these bacteria from anchoring to the cells that line the urinary tract. 

A urinary tract infection (UTI) is a common type of infection that occurs when part of the urinary tract becomes infected, usually with bacteria. UTIs are more common amongst women than men and it’s estimated that about one in two women have at least one UTI during their lifetime. The most frequent culprit in UTIs is a type of E. coli specially designed to cause infection. E. coli are common bacteria found loitering harmlessly in most people’s guts and make up part of the good beneficial flora. However, specialised forms of E. coli called, uropathic E. coli, have the ability to make a home within the urinary tract environment, where they can cause infections ranging from cystitis to pyelonephritis (a serious kidney infection).

Bacterial specialisation

Uropathic E. coli are covered by small hooks called pili or fimbriae, which are actually the bacterial equivalent of Velcro®, allowing them to attach themselves to the wall of the bladder and urethra. Once they attach, they can start reproducing as a prelude to infection. Your body tries to stop this by making the cells in the urinary tract slippery – rather like a biological form of Teflon®. However, the E.coli have very strong ‘Velcro®’, enabling them to anchor themselves tightly, preventing them from being washed away by the flow of urine. A growing problem is that uropathic E. coli are developing a resistance to antibiotics, some of which have been the mainstay of treatment for UTIs. This emergence of antibiotic resistance makes successful therapy of this infection more difficult. So, better methods of non-antibiotic prevention and treatment are needed. Some examples of non-antibiotic prevention methods that have been under investigation include the use of probiotics and cranberry products. 

Cranberries are native to North America and were used for centuries as food and medicine. Native Americans used cranberries for their antibacterial properties and even make mention of their use in urinary disorders. Until now, scientific studies revealing the mechanisms by which cranberries help fight UTIs have been lacking. However, a new study has determined the physical mechanisms by which cranberries exert their effects, proving that they really do work. 

A team of researchers led by Terri Camesano, professor of chemical engineering at Worcester Polytechnic Institute, used a tiny probe to measure the strength of the bond between the infection-causing bacteria and urinary tract cells. The results, published in the journal Molecular Nutrition & Food Research, showed that the ability of the bacteria to attach themselves to the human urinary tract cells decreased as the concentration of cranberry juice increased. A point was reached when the attachment force was so weak that the E. coli could be washed away by the force created by the flow of urine through a person’s urinary tract. 

How does cranberry juice achieve this?

Cranberries are rich in a chemical called proanthocyanidin that has anti-inflammatory and antioxidant activity. But studies have also shown that proanthocyanidins force the fimbriae on uropathic E. coli to curl up, reducing their ability to attach to urinary tract cells. This effect has also been seen with drug-resistant bacteria, so, even if prescription antibiotics won’t kill the bacteria due to resistance, proanthocyanidins could still prevent them from attaching to the urinary tract cells. 

So, for those who suffer from frequent UTIs, cranberry products may offer a simple and safe alternative strategy to protect against those uncomfortable trips to the pharmacy.  


Article References

Liu Y, Pinzón-Arango P, Gallardo-Moreno A, Camesano T. Direct adhesion force measurements between E. coli and human uroepithelial cells in cranberry juice cocktail. Mol Nutr Food Res 2010; Jun 21. [Epub ahead of print]

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