Cranberry flavonoids block bacterial adhesion

American scientists have revealed new impacts of cranberry juice on bacterial infections. The results open up new, interesting possibilities for antibiotic drug development.

Antimicrobial resistance, e.g. microbes that are resistant to current antibiotics, is one of the main threats for the future's health care system. At least 2 million Americans are infected each year with drug-resistant bacteria, while some 23 000 die from those infections. Therefore scientists are trying to identify potential new antibiotic drug targets.

In order to cause an infection, bacteria must first adhere to a host and accumulate in sufficient numbers to for a biofilm. A biofilm is a group of bacteria in which cells stick to each other and often these cells adhere to a surface. The new study reveals that compounds in cranberry juice called flavonols greatly reduced the ability of the bacteria E. coli to stick to a surface. E. coli bacteria cause many types of infections, including urinary tract infections.

Previous study has shown that cranberry proanthocyanidins play a role in cranberry juice's ability to block bacterial adhesion. In the new study, advanced chemical techniques were used to separate and characterize cranberry juice constituents. E. coli cells were cultured in samples of juice, and atomic force microscope was used to measure the bacteria's ability to bond to a surface. After the first round of testing, samples that showed the greatest ability to reduce E. coli adhesion were further fractionated.

Tests found that flavonols significantly reduced E. coli adhesion. Flavonol galactosides showed the strongest results. Previous study has shown that cranberry juice compresses the tiny tendrils (fimbriae) on the surface of the E. coli bacteria. Tendrils enable bacteria to bind tightly to the lining of the urinary tract. The change in shape reduces the ability of the bacteria to stay long enough to initiate an infection. Also flavonols are likely to affect the ability of fimbriae to bind to surfaces, but in a different way than proanthocyanidins do.

Like proanthocyanidins, flavonols are part of cranberry's defence system. They are secondary metabolites that are produced in greater concentrations when the plant is under stress or in the presence of pathogens. The study showed that not only proanthocyanidins but also other classes of cranberry compounds, such as flavonols, have anti-adhesive properties. These may have implications for development of alternative antibacterial treatments.

Author's comment: Most of the health benefits of cranberries have been studied on American cranberry (Vaccinium macrocarpon), which is related to Finnish bog cranberry (Vaccinium oxycoccos) and small cranberry (Vaccinium microcarpum). According to USDA proanthocyanidin database, the proanthocyanidin contents of American cranberries are similar to those of Finnish cranberries.

Anni Koskela, Arctic Flavours Association

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virtsatieinfektio  bakteeri-infektio  flavonolit  karpalo  proantosyanidiinit  cranberry  proanthocyanidins  flavonols  bacterial infection  urinary tract infection