Cranberries crush bacteria's communication networks

Fruit or bacteria-fighting power pills?(Credit: 5PH/Depositphotos)

They might not be as fashionable among the hipster set as kale but cranberries' health properties are undisputed. Long known as a remedy for urinary tract infections, they have in recent years also been shown to benefit our gut, heart, immune system and brain. And now, a new study has revealed that these berries might just be able to succeed where conventional antibiotics are struggling: stopping bacterial infections from spreading by disrupting the pathogens' communication networks.

Current antibiotics treat infections by killing the bacteria, which results in increased selective pressure to develop resistance. Put another way: If something was trying to kill you, wouldn't you find a way to protect yourself too?

This has led to one of the biggest public health threats today – growing bacterial resistance to antibiotics. Indeed some bacterial infections have developed resistance to multiple drugs, making it increasingly difficult to find an effective treatment. An example would be those caused by the Pseudomonas aeruginosa, a common strain that attacks compromised body tissues. It is usually found in hospitalized patients and those with a compromised immune system. According to the Centers for Disease Control and Prevention (CDC) in the United States, more than 6,000 (13 percent) of the 51,000 healthcare-associated P. aeruginosa infections that occur each year are multi-drug resistant. And every year, they claim the lives of some 400 patients.

This state of affairs has given rise to the need for alternative antibiotic treatments that inhibit bacterial growth without killing them and causing an increase in selective pressure. One such method lies in inhibiting quorum sensing (QS), or to put it simply, the bacterial cells' ability to communicate with one another. When bacteria enter a body, they 'talk' to each other using signaling molecules that enable them to co-ordinate their behavior to adapt to environmental changes, evade the host's immune response and establish a successful infection. It follows then, that disrupting their communication networks should stall their growth.

In Canada, scientists from McGill University and INRS-Institut Armand-Frappier are working on one such solution using a cranberry extract rich in compounds known as proanthocyanidins (cerPAC). While previous research has shown how they have prevented bacteria from sticking to the walls of the urinary tract as well as impaired the mobility of certain pathogens, the scientists wanted to find out how effective they would be managing bacterial infections as QS inhibitors. Tests were conducted on fruit flies, which were infected with a P. aeruginosa strain and fed the cranberry extract.

The results were promising: Not only did the flies that were fed the cranberry extract survive the bacterial onslaught, scientists also found that the cerPAC compound was successful in disrupting two QS molecules in the P. aeruginosa bacterial cells, 3-oxo-C12-HSL and C4-HSL.

"Cranberry PACs interrupt the ability for bacteria to communicate with each other, spread and become virulent," said study author Dr. Eric Déziel of INRS-Institut Armand-Frappier. "The cranberry extract successfully interferes with the chain of events associated with the spread and severity of chronic bacterial infections."

More importantly, they did so without killing the bacterial cells, which means the method might avoid the cycle that leads to antibiotic resistance.

While further tests are needed to ensure that the extract doesn't elicit a toxic response in humans at the concentrations used, the results so far suggest that there is potential for cerPAC to be used in the treatment of acute and chronic infections caused by P. aeruginosa and other bacterial pathogens.

The team's results were published in Nature.

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